We already state in the manual to turn off unecessary programs and background tasks.
It may be useful though to figure out which common background tasks cause problems, if any.
A standard one that causes the game to go slow and jittery for me at least is Norton's sheduled weekly anti-virus scan. (the clue whn playing full screen is the hard disk starts chittering away like crazy
!. This anti-virus scan does NOT seem to realise that the end user is currently playing a full screen DirectX game (I have had it go off when playing e.g. the Sims2).
the other suspects I have is thewindows disk catalogue function (A worthless item one can turn off). This trolls your hard drive to make searching for items allegedly faster (though I have not noticed any speed decrease since I turned it off).
To turn off this catalogue function. Open explorer, find the drive and right click, under properties (General) is a check box for "Allow indexing service to ... for fast disk searching" - uncheck that, and you have better general performance, with only a slight (IMHO) slwdown in searching.
Xp tends to do these things in "idle" mode - and it seems to consider a full-screen DirectX game "idle mode" (it is blind to the process?), whereas 98 did not.
Cheers
Andy