.htaccess for multiple applications?

[eluser]Rein Van Oyen[/eluser]
Thanks again ChrisMiller! I appreciate all your help.

I fully understand the code and that's indeed what I need. But after pasting it in my .htaccess. Every http request to the domain still gives a 500 internal server. When I comment out following lines, the 500 error is gone. I need those lines, tho.

Code:

RewriteCond %{REQUEST_URI} !admin/$
RewriteRule ^(.*)$ /admin.php/$1 [L]

I don't have any clue on why these don't work...My error log says something about too much requests. Am I creating an infinite loop here? Is there any way that this could be because of my CI configuration?

Thanks in advice,
Rein