BF2S Forums Virus and trojan assistance

So my dad was working on our XP computer yesterday, while running a virus scan, and suddenly it found something. Around this time, something popped up on Zone Alarm saying "mavvsnet.tmp is trying to access the internet". Since this sounded like a virus or trojan, I obviously said no, and decided to completely kill that computer's internet access through my router. We decided to reboot shortly thereafter, as the computer froze, and explorer.exe would crash every thirty seconds. So I started up and went into safe mode, where I ran Malwarebytes Anti-Malware, while still dealing with the explorer.exe problem (this time, it would try to restart every thirty seconds, popping up the "This is safe mode..." message consistently). After the MBAM scan finished, I found that there was something called "trojan.vundo.h", which I obviously removed. I restarted into safe mode again, and ran MBAM again, with a full scan. The explorer.exe problem had ceased, and the scan found a couple of more registry problems, but it removed those. I thought it was clear, but, when I restarted into normal windows, all of my operating system settings had been completely reset, as if I had just installed the OS again. There were no restore points before December 12, the picture was the default picture, the time was showing, the theme was blue, and My Documents and My Computer were not displayed on the desktop. However, all my documents appeared fine, and it looked as if nothing had been ruined but the operating system. Naturally, I am still a bit wary about the safety of my computer. So, two questions. What else should I run to ensure it is again safe to use the computer for important stuff like internet monetary transactions and Newegg purchases? What caused only the OS to appear messed up? All help is appreciated.