I want to display b2evolution caregory list like a tag cloud. For example http://www.eatdrinksleepmovabletype.com/tutorials/building_a_weighted_category_list/

I don't know how to do that, I only know that I have to change _categories.php (and I'm not sure)

I got it!
Based in the information of the link below, I change _categories.php file to get a Category cloud (like technorati, del.icio.us) based in the number of posts of categories. To use it, the only thing you have to do is change the _categories.php of your skin for this. Here is the code:

<?php
	/**
	 * This is the template that displays (recursive) list of (sub)categories
	 *
	 * This file is not meant to be called directly.
	 * It is meant to be called by an include in the _main.php template.
	 *
	 * b2evolution - {@link http://b2evolution.net/}
	 * Released under GNU GPL License - {@link http://b2evolution.net/about/license.html}
	 * @copyright (c)2003-2005 by Francois PLANQUE - {@link http://fplanque.net/}
	 *
	 * @package evoskins
	 */
	if( !defined('DB_USER') ) die( 'Please, do not access this page directly.' );

	# You can customize the following as you wish:
	if(!isset($cat_all)) $cat_all = /* TRANS: All categories, skin's categories list */ T_('All');	// Set to empty to hide
	# global category list delimiters:
	if(!isset($cat_main_start)) $cat_main_start = '<p>';
	if(!isset($cat_main_end)) $cat_main_end = '</p>';
	# Category delimiters:
	if(!isset($cat_line_start)) $cat_line_start = '';
	if(!isset($cat_line_end)) $cat_line_end = ' ';
	if(!isset($cat_line_checkbox)) $cat_line_checkbox = false;
	# Category group delimiters:
	if(!isset($cat_group_start)) $cat_group_start = '';
	if(!isset($cat_group_end)) $cat_group_end = '';
	# When multiple blogs are listed on same page:
	if(!isset($cat_blog_start)) $cat_blog_start = '<h4>';
	if(!isset($cat_blog_end)) $cat_blog_end = '</h4>';	

	/*
	 * WARNING: the category list is displayed recursively.
	 * This is a little tricky. Don't modify below unless you really know what you're doing!
	 */
	
	// ----------------- START RECURSIVE CAT LIST ----------------
	cat_query();	// make sure the caches are loaded
	if( ! isset( $cat_array ) ) $cat_array = array();
	
	/**
	 * callback to start sublist
	 */
	function cat_list_before_first( $parent_cat_ID, $level )
	{	// callback to start sublist
		global $cat_group_start;
		if( $level > 0 ) echo "\n",$cat_group_start,"\n";
	}
	
	/**
	 * callback to display sublist element
	 */
	function cat_list_before_each( $cat_ID, $level )
	{	// callback to display sublist element
		$a = 5;
		$b = 10;
		$c = 15;
		$d = 20;
		$e = 25;
		$f = 30;
		$g = 40;
		global $blogfilename, $cat_array, $cat_line_start, $cat_line_checkbox;
		$cat = get_the_category_by_ID( $cat_ID );
		echo $cat_line_start;
		if( $cat_line_checkbox )
		{	
	
			echo '<label><input type="checkbox" name="catsel[]" value="'.$cat_ID.'"';
			if( in_array( $cat_ID, $cat_array ) )
			{	// This category is in the current selection
				echo ' checked="checked"';
			}
			echo ' />';
		}
		if ($cat['cat_postcount'] <= $a ) {
		echo '<span style="font-size: 75%;"><a href="'.url_add_param( get_bloginfo('blogurl'), 'cat='.$cat_ID ).'">'.format_to_output($cat['cat_name'], 'htmlbody').'</a></span>';
		} elseif ($cat['cat_postcount'] <= $b ) {
		echo '<span style="font-size: 100%;"><a href="'.url_add_param( get_bloginfo('blogurl'), 'cat='.$cat_ID ).'">'.format_to_output($cat['cat_name'], 'htmlbody').'</a></span>';
		} elseif ($cat['cat_postcount'] <= $c ) {
		echo '<span style="font-size: 125%;"><a href="'.url_add_param( get_bloginfo('blogurl'), 'cat='.$cat_ID ).'">'.format_to_output($cat['cat_name'], 'htmlbody').'</a></span>';
		} elseif ($cat['cat_postcount'] <= $d ) {
		echo '<span style="font-size: 150%;"><a href="'.url_add_param( get_bloginfo('blogurl'), 'cat='.$cat_ID ).'">'.format_to_output($cat['cat_name'], 'htmlbody').'</a></span>';
		} elseif ($cat['cat_postcount'] <= $e ) {
		echo '<span style="font-size: 175%;"><a href="'.url_add_param( get_bloginfo('blogurl'), 'cat='.$cat_ID ).'">'.format_to_output($cat['cat_name'], 'htmlbody').'</a></span>';
		} elseif ($cat['cat_postcount'] <= $f ) {
		echo '<span style="font-size: 200%;"><a href="'.url_add_param( get_bloginfo('blogurl'), 'cat='.$cat_ID ).'">'.format_to_output($cat['cat_name'], 'htmlbody').'</a></span>';
		} elseif ($cat['cat_postcount'] <= $g ) {
		echo '<span style="font-size: 250%;"><a href="'.url_add_param( get_bloginfo('blogurl'), 'cat='.$cat_ID ).'">'.format_to_output($cat['cat_name'], 'htmlbody').'</a></span>';
		} else {
		echo '<span style="font-size: 300%;"><a href="'.url_add_param( get_bloginfo('blogurl'), 'cat='.$cat_ID ).'">'.format_to_output($cat['cat_name'], 'htmlbody').'</a></span>';
		}
		if( in_array( $cat_ID, $cat_array ) )
		{	// This category is in the current selection
			echo "*";
		}
		if( $cat_line_checkbox )
		{
			echo '</label>';
		}
	}
	
	/**
	 * callback to display sublist element
	 */
	function cat_list_after_each( $cat_ID, $level )
	{	// callback to display sublist element
		global $cat_line_end;
		echo $cat_line_end,"\n";
	}
	
	/**
	 * callback to end sublist
	 */
	function cat_list_after_last( $parent_cat_ID, $level )
	{	// callback to end sublist
		global  $cat_group_end;
		if( $level > 0 ) echo $cat_group_end,"\n";
	}
	
	// Start global list:
	echo $cat_main_start;
	if( $blog > 1 )
	{	// We want to display cats for one blog
		echo "\n",$cat_group_start,"\n";

		if( !empty( $cat_all ) )
		{	// We want to display a link to all cats:
			echo $cat_line_start,"\n";
			echo '<a href="',get_bloginfo('blogurl'),'">',$cat_all,'</a>';
			echo $cat_line_end,"\n";
		}

		cat_children( $cache_categories, $blog, NULL, 'cat_list_before_first', 'cat_list_before_each', 'cat_list_after_each', 'cat_list_after_last', 0 );

		echo "\n",$cat_group_end,"\n";
	}
	else
	{	// We want to display cats for all blogs
		for( $curr_blog_ID=blog_list_start('stub'); 
					$curr_blog_ID!=false; 
				 $curr_blog_ID=blog_list_next('stub') ) 
		{ # by uncommenting the following lines you can hide some blogs
			// if( $curr_blog_ID == 2 ) continue; // Hide blog 2...

			if( ($curr_blog_ID == 1) && empty( $cat_all ) ) continue; // Hide blog 1 if requested

			echo $cat_blog_start;
			?><a href="<?php blog_list_iteminfo('blogurl', 'raw') ?>"><?php blog_list_iteminfo('name', 'htmlbody') ?></a>
			<?php
			echo $cat_blog_end;
	
			// run recursively through the cats
			cat_children( $cache_categories, $curr_blog_ID, NULL, 'cat_list_before_first', 'cat_list_before_each', 'cat_list_after_each', 'cat_list_after_last', 1 );
		}
	}
	
	// End global list:
	echo $cat_main_end;

	// ----------------- END RECURSIVE CAT LIST ----------------

?>

You can change the number of posts necesary to the different weight of the fonts here:

$a = 5;
		$b = 10;
		$c = 15;
		$d = 20;
		$e = 25;
		$f = 30;
		$g = 40;

I thing i will be interesting to know blogs total post to change this values dinamically. Can someone help how get blog total post?

Thanks and sorry for my english!

interesting.

Can you give a screenshot how it will look like after?

Thanks. :)

Will this work in 1.8.1? If not, is there a way to make it work?

:) I'm guessing the answer is no?

The answer is: try it.. :)

:) I have! But, the category plugin is sufficiently different from the old category structure that this hack does not apply. I would need to understand a great deal about plugins before I could adapt this hack to one.

I created a Plugin for b2evolution 1.8 that displays a tag cloud:

http://blog.wannawork.de/index.php/2006/11/10/tag_cloud_plugin

I just installed it, and it works great-- thank you!