Welcome to the forum.

There's a [url=http://b2evo.sonorth.com/show.php/feed-importer-pro-plugin]commercial plugin[/url] that can export posts saving all comments, properties and custom fields, it can easily move posts between blogs.

You can also try to dump the database and import posts and their categories manually. This requires some b2evo and SQL knowledge, though.

BTW if you are talking about the same b2evo instance, you can easily move categories (and their posts) between blogs.
Just enable this setting in /conf/_advanced.php

Thanks for the reply, I am indeed trying to transfer between blogs in the same b2evo instance, but I can't see which is the right setting to change.

Can you recall what the setting is called?

Thanks :)

Well, the setting is in /conf/_admin.php actually :)

$allow_cross_posting = 3;

Haha - I'd just found it!

Now to try it - many thanks for the help :)

.... and that is working perfectly.

Thank you for the prompt help!

No problem ;)