Is the scenario I described in the beginning possible?
Are there any other side effects besides the ones I am aware of?

If you want to keep old links to media files use rewrites in .htaccess
/media > /__b2evo/media
This is easier than edit the database even if you don't care about image links.

Is there a way to deal with the wrong paths to images without relying on SQL queries? I prefer not to interfere with the database because I am not fully aware of the relationships between the tables in the database schema - so I think this is a place where I can easily screw something up :-)

Simple replace query in evo_items__item table will not do any harm to b2evo structure as long as you only edit post_content.

A drawback is you will see b2evo admin, skin files and /rsc files in /__b2evo subdirectory. If you want to completely hide /__b2evo path rewrite all requests with .htaccess, you'll find lots of manuals about it in google

Thank you for the quick response; I'm sorry for not reacting earlier (life threw me some undocumented exceptions).

The method described above works, but there are some side effects I did not consider. What happens is that the page opens and the stuff is rendered correctly, but if I try to post a comment - some files cannot be found.

I figured that the base_url needs to be changed too, so there's a new step in those instructions:

1. Copy b2evo's files to to /__b2evo

2. Copy index.php to /

3. Change index.php "require_once dirname(__FILE__).'/conf/_config.php';" to "require_once dirname(__FILE__).'/__b2evo/conf/_config.php';"

4. Change basic_config.php "$baseurl = 'http://site.net/';" into $baseurl = 'http://site.net/__b2evo/';

[/list:o] After that, everything works, but there is a side effect: all the URLs have "__b2evo" in them, so all the old links are broken.

If you want to keep old links to media files use rewrites in .htaccess

Indeed, I forgot about mod_rewrite, thank you for the suggestion. Here is the .htaccess I am using, it is placed in the root directory of my site (where I now copied index.php from /__b2evo)

RewriteEngine On
#RewriteLog   "~/tmp/rewrite.log"
#RewriteLogLevel 3
RewriteRule (.*)/media/(.*) $1/__area51/media/$2

However, it does not work. Hmmm... The mod_rewrite log is not created either, so I am a bit puzzled. Further assistance will be greatly appreciated.