System Restore

My bro downloaded some annoying virus 2 my system, it kept stopping my AVG virus checker... So to get rid of it i did a system restore back to the date the operating system was installed... I redownloaded AVG it this time did a full scan and found nothing... but im still not sure if my system is clear... Is there any other checks/procedures i should do... OH and another problem ive got XP service pack 2 and i can only find my XP service pack 1a disk, and for some reason it wont let me downgrade how do i go about deleting 2 and wacking on 1a...

Thanks for any help you can give me geeks

 

In answer to the first question: http://forums.majorgeeks.com/showthread.php?t=35407, and to the second part about SP2,http://www.majorgeeks.com/Dariks_Boot_and_Nuke_CDRCDRW_Version_d4596.html
Hope this helps!