You seem to be on the right track with disabling everything from boot via msconfig. However, if windows is giving you too much trouble, as always, format and reinstall. If you have several disks, chances are windows only exists on one of them. And if you dedicate a drive towards backups, you have a few dvd copies laying around? (hopefully).
Windows is a disposable operating system. It's basically intended to be reinstalled multiple times. While, yes, it is possible to save basically anything (hence the server versions), it's not always worth the effort unless you have something that can not be replaced (like data).
While I'm keeping myself on some sort of leash here, your airhead girlfriend should never use a computer that has any sort of importance, especially when it has anything to do with social networking sites. My friends and family all understand that my computers are hands off, and if you need to do anything, you're going to be using my laptop (OpenBSD, Athlon 2400+, 512MB DDR1, 120GB HD), under a restricted guest account.
To actually remedy your problem, good luck. My suggestion would be stopping all files from booting, absolutely everything. Anything that boots after that, google the process name and find out what it's purpose is. If it's useless, oust it. If you can't easily remove it, google some more and find out what it takes to remove it (MSBLASTER, for instance, was a particularly difficult bitch to remove, you actually had to download a removal program).
http://www.processlibrary.com/ is a good resource to find out what should and shouldn't be running (check the program names from within taskmgr). If you still can't win over the virii, try a few of those hit-or-miss programs like hijackthis and antispyware-what-ever-the-fuck. If you can uninstall it easily, it's usually not worth the effort, format and start new again.
