is it malware?

I am working my way through all the step, though I may have problems downloading some of the tools.

the system
windows xp\w service pack 2
mostly use firefox browser, explorer sometimes

the problems.
system seems a little slower.
have had lots of trouble downloading any files ie. system tools games
recently the window has started bobbing up and down like i am scrolling ( on its own)
tried loading a game from disk after these other problem started and get the following error c:\windows\system32\cmd.exe
the ntvdm cpu has encountered an illegal instruction
cs:coooip;4487 op;06 10 88 3c 1f choose close to terminate the application

have used avg antivirus, found nothing
mcafee internet security suite, found nothing ( uninstalled per instructions of one antivirus)
webroots spy sweeper, found nothing
avg rootkit, found nothing

well it will take me a few days to get through the rest of the steps but am I wasting my time? is it something else?

thank you in advance for any help. DOM