I work for a large network security firm, your problem is a virus that affects certin drivers in the computer and trys to replace them. First download and install HijackThis (http://free.antivirus.com/hijackthis/) Scan your computer you should find the virus and beable to rid it from your system. If that does not work try VundoFix (http://www.tinyurl.com/9uaag)
This is a very tricky virus to get rid of depending on how it has manifested, you might want to do a clean install of windows to be safe.
As far as y only 2gb of memory run stable is due to the curroption of the drives that are first loaded from boot up, the virus occupies certin parts RAM and when windows xp is loaded into ram im guessing you have a lot of start up programs, there for the virus will not load in inital start up, to begin the curroption of the driver files.
Hope you get your problem fixed! Cheers