Yeah, doesn't sound great. My guess is that something became corrupted in your system. What you ultimately want to do is backup your system, fix any detectable errors, update your s/w, and as a last resort reload your system.
Imho, the most important thing you can do right now is back up your system. Save any files you do not wish to lose. Burn them to a CD or DVD, or back them up to an external drive, but back them up. You should suspect that your system is corrupted and you could lose all of your files.
After you backup your system, you should run Disk Utility and do a Verify on your hard drive. If it comes out clean, that's good if not exactly helpful to identify the problem. If it comes out with errors and you must repair via your installation media, the thread below includes a discussion on how to do that:
http://www.mac-forums.com/forums/showthread.php?t=63755
Next, make sure you're running the latest s/w. Get the latest updates for your s/w, including the OS (Menu Bar: Apple> Software Update...), FireFox, iTunes, and Adium.
At that point you're probably going to be doing as well as possible w/o reloading your entire system. Doing a complete reload is drastic and probably unnecessary. I say "probably", allowing for a small possibility of needing to do so. If you've been running for any amount of time with a corrupted system, errors can propagate through the system, and that's a Bad Thing.
Try the other things first and post your results. Good luck!
