Oh GOD! You saved my life! I was just about to open a new thread, but then I decided I'd better check if there was already a topic that might help me out.
Just for the record, I want to say what was my problem, so that if someone ever has a similar problem, they might find the solution in here:
I'm running wordpress in my site for newsposting, everything was great, but for some odd (and very stupid) reason, I changed the "WordPress address (URI)" and the "Blog address (URI)" from the normal http://www.mydomain.com to http://www.mydomain.com/index.php (I know... it was just wrong!)
Why would I do that? I don't know... it's a long story, but the point is that I changed it and after that, I couldn't do anything from the admin panel! I mean, I couldn't even enter it! And my site looked weird (it didn't have access to my stylesheet)... Apparently, I managed to get everything under the "index.php/" directory... *sigh*
I was terrified, but then I took a look to that guide macmanx mentioned in the post above and I manage to change the values in the database and now everything's back to normal.
Well, I wanted to thank you and to tell my 'story' in case someone else has a similar problem later on (although what I did was terribly stupid...)