You should try and search for the sasse virus and try to remove it manually, or you can download the sasser removal tool from symantec (
HERE ).
Also when you install your Windows XP it helps to unplug your network cable, if you connect to the internet through the network card for example, since your computer can be attacked and can get infected before the XP installation even finishes.
Also before downloading anything or before you even connect to the internet turn on the XP firewall, since from default is not turned on.
Hope this helps.