There is a well regarded site http://www.musicxp.net that gives tips for optimizing XP for DAWs. I have used the tips there for both my boxes and for friends and I have found the tips to be outstanding. My computer runs glitch free and there was a noticeable difference in performance after tweaking. If you have not looked at the site before it is time worth taking to optimize your system.
We are the music makers, we are the dreamers of dreams …
24" 2.4 Ghz iMac, OSX 10.4.10, MOTU 828 MKII, 2 Glyph 250 Gig external drives, Logic 9, Finale 2008 GPO, JABB, Strad, Gro, Reason 4, EWQL Storm Drum, Adrenaline, Symphonic Choirs, SO Gold,All Arturia Synths, Many NI Synths, Spectrasonics Synths, KH Strings, VEPro on a Windows 7 4x 2.8 Ghz 12 gig of RAM