Oh, boy, that's pretty serious. Let's see...
The first thing you should do is reboot into Safe Mode with Networking (holding F8 before the Vista loading bar appears should show the menu with this option). When you're presented with the Welcome Screen, choose the Administrator account (the actual Administrator account). With any luck, this account shouldn't be locked out of anything. Hopefully, whatever it is that hit you won't be running in Safe Mode, but that's not guaranteed.
Now, head over and grab
Malwarebytes' Anti-Malware, install and run it (let it update). Scan your computer with it and remove anything it finds. Next, grab
Spybot: Search & Destroy and install it. Let it update, and do a full scan of your system, removing anything that you find.
Regardless as to what antivirus software you're using, you're going to want to completely remove it, since it's been compromised in the worst possible way here. I'd recommend downloading
AVG Free and giving your system a good scrubbing with it afterward, but I should note that you need to do this from normal mode.
Once all that is done, you're going to want to run a file check to be sure that you Windows files aren't corrupt. You need to be in normal mode to do this, so reboot first if you haven't already. Begin by holding the Windows key and pressing R. This should pop up the Run dialogue box. In this, type
sfc /scannow and hit enter. You will need your Vista disc to restore any corrupted files it finds. Once this is done, Windows, at least, will be at its core good to go. I must warn you that these things might not fix everything; If not, then you may be looking at a more in-depth look, or maybe even a backup and format of your hard drive.
Depending on your skill with the computer, you may be able to do more, but I'm not confident in recommending an attempt if you're not familiar with how Windows works. If you are, however, download
Autoruns, which will give you fine control over everything attached to your system, including drivers and other things that are normally hidden. Be very careful when using this program - While it can do a lot of good, it can do a lot of harm if you disable the wrong things. A coworker of mine once disabled both the video driver
and the VGA fallback driver. That was a fun trip to the recovery console. In the case that an entry in Autoruns won't remove even in Safe Mode, you'll need to take note (using a pencil and paper) the full path and filename of each of those entries. Once done, boot from your Vista disc and choose to repair, and then choose to open a command prompt. Go to each path, and delete each file. Once that's done, reboot, and clean up the mess. With that done, you should be good to go.
... OK, OK. If you find that the above isn't working and you're not willing or able to backup/format, then there IS one thing that you can do that would allow me to see what you see when you run Autoruns, which in turn should be able to let me tell you what to remove. After Autoruns is up and running, and after the list has been completely built, go to File, then click Save... - Save the .arn file, and upload/link it here. I'll be able to see your entries, and tell you what's good and what's not.
