Here is a recent article about a current trojan running through facebook.
Facebook Users Attacked by Trojan Virus :: Schipul Blog

I suggest you start you computer in safe mode and run current versions of anti-spyware and anti-virus software.

Here are a couple I like.
AVG Free - Download AVG Anti-Virus Free Edition for Windows XP and Vista
The home of Spybot-S&D!
Ad-Aware 2008 Free - Lavasoft

To boot in safe mode. A description of the Safe Mode Boot options in Windows XP

1.Restart your computer and start pressing the F8 key on your keyboard. On a computer that is configured for booting to multiple operating systems, you can press the F8 key when the Boot Menu appears.

2.Select an option when the Windows Advanced Options menu appears, and then press ENTER.

3.When the Boot menu appears again, and the words "Safe Mode" appear in blue at the bottom, select the installation that you want to start, and then press ENTER.

I'd suggest following the directions from squirrelnmoose from the earlier posts as your problem sounds almost exactly like mine and I do use facebook so I mightve gotten the antivirus2009 malware from the site. Hope your problems get fixed the direction from earlier on this thread really did help me. Good luck!

When I get that mess, I run a C-search for everything in the intruder's title...
Then I carefully check-out what was found, in properties, and on the Net, before I uninstall and/or delete what the search found...

When you have a "mad-monkey" intruder in the PC, always run an internet search on it, to read what others are saying about it... Like you should always do with unknown emails, before you open them, if you must open them...
With questionable emails, surf the name or email address, adding the words "scam, virus" to the search words... Make it a habit... Change from IE and OE, to SeaMonkey... It's faster and cleaner, and a lot more secure... IE is a hacker-target... I set a firewall to block IE from the Internet...

Sometimes you can find those bad-things in Control Panel's "uninstall programs"...

Sometimes running a system restore to an older registry backup will eradicate the problem.. but sometimes that can seriously mess-up your latest installs, updates, and files... Before running a restore, make a CD-RW backup of all your treasures.. including favorites (or bookmarks), music, videos, files, and pix...