|I'm wondering if it infected the Master Boot Record or Master File Table rather than BIOS. The latter is difficult to infect as it would have to flash microchips. You may of-course have some info that pointed to BIOS and even the unlikely is not impossible.|
MalwareBytes and/or SuperAntiSpyware are useful to have onboard so that you can hit a virus pronto if you get one. Even running CCleaner frequently can help because viruses are often put into Temporary Internet Files at first.
As for AV's, well Avast often gets good reports. Unfortunately there are always going to be viruses that might be picked up by one AV rather than another, so its tricky to be adament. It is not really on to have more than one AV running in real time because they can check each other and cause conflicts.
SpywareBlaster is good to have because it gives protection without running in the background (it puts kill bits in the registry to block nasties).
There is one thing that I believe all XP users should have onboard unless they want to run all the time with the nuisance of limited rights. It is the relatively little known "Drop My Rights" and is from MS. It is a very small program that again doesn't run in the background. It is actioned by creating a two stage shortcut to your Browser(s). It lowers your rights when browsing which means the "nasties" have low rights too, so are less likely to take. Very easy to put in and I have only found three rare instances when you will notice its existence. I can list these instances and give you more info and ideas if you decide to go that way.
I don't know which particular virus hit you but maybe someone else will have an idea. It obviously went very deep into your computer.
Always pop back and let us know the outcome - thanks