Firstly really sorry for not coming back here, been really busy with business work.
Right shall we get back to the topic
You can get viruses from any kind of websites, regardless of forums,auction sites or p2p, torrent websites. There are endless possibilities of getting viruses. The only strange thing I found from first your post was that you didn't mentioned that you use P2P software but still getting viruses. That made me think either you have bought or used either floppy disk, infected CD or infected USB key or infected SD card, which might have caused this. Additionally it could have been an external link you clicked either on Myspace, Ebay or this forum which might have lead you to another website which had potential virus. This does not mean that this forum, Myspace or Ebay is infected however it could be the destination site which might have been infected. Unless you provide a log, it is very hard to find out where you got the virus from.
You see the problem is that, people are unaware that they can get viruses from any kind of electronic source regardless of websites. As I mentioned above it could have been from a CD, USB or SD cards.
The only way of protecting yourself against these viruses is to install Antivirus, Antispyware, AntiRootkit, Firewall and Antispam. Then keep them updated all the time. Then run them every week or so (most probably when you are not using your computer).
In other words, you need to take care of your computer just like you take care of your horse. In terms of horse, Food, medicine and extensive training makes your
Horse fit and healthy. Similarly with computers, scanning, updating and cleaning, defragmenting your pc will make your pc run faster.
AVG Free edition is a almost good antivirus however if you click on the options tab you'll see it does not have Antirootkit enabled. Rootkits can be very dangerous, some get installed onto your computer like your computer drivers. Taking them out is very hard and time consuming. I'd say get AVG pro or AVG internet security which works alot better.
Saying that AVG alone cannot work properly, you should install Spybot Search and Destroy and Malwarebytes. Additionally you can use CCleaner or WinXP Manager to keep your pc clean. You can use Diskeeper to defragment your pc.
I'd like to say more but I have to get back to work
, however will post more later.