I've seen a few help topics like this one but mine only relates to In-Game lag not lagging offline or just on windows itself.
When I play Call of Duty 2 online every few seconds there's a lag spike, but my ping is fine. I guess it's more of a skip, the sound skips as well it happens about every 3 seconds and in a pattern not at random. Which makes it really annoying and hard to ignore when playing. This also happened a few times when playing America's Army but not as much. Sometimes the game is fine though last night i was playing fine but I went on a few hours ago and it wouldn't go away.
I also have Medal of Honor and it doesn't happen at all with that game.
It's not my system my specs are:
-256mb PCI-E graphics
-1.5 GB ram
-320 GB of HDD
-ATI Mobo
-Windows XP Pro sp2

Again this only happened recently, it happened with BF2 a while ago but I uninstalled that ages ago. And I haven't installed any new software since this started occuring again. Just ran a virus scan and it comes back clean.
Thanks for your help COD2 is a great game and hopefully ill be able to get back into the action.

ok now the audio is skipping for everything on my PC not just games (ie movies and songs)

Update your sound and video card drivers, if you haven't already.

Clean up your drive using Disk Cleanup (on XP home it is start>all programs>accessories>system tolls>disk cleanup).

Defragment your drive (Start>All Programs>Accessories>System Tools>Disk Defragmenter)

http://www.techspot.com/vb/topic57112.html

http://www.techspot.com/vb/topic65943.html

http://www.techspot.com/vb/topic58138.html

This is all of my knowledge. Good luck!

Okay I did a virus scan and nothing came up, i defragged, "cleaned up" the disk, and reinstalled itunes.
(Music works fine in windows media player but not in itunes)
But now i'm still getting the lag in the game, itunes skips, and my computer is really slow...(keep in mind i have 1.5gb of ram and am only using 30% of my internal HDD.
My friend told me it could missing or corrupt system files, is there something that i can download that will check if i have all of the neccesary system files and if any are corrupt? I dont have the xp pro installation cd, it came preinstalled but i do have a xp home installation cd.

Have you tried updating your drivers?

yes, both sound and video are updated

Have you tried uninstalling ITunes and making sure its not that?

yea i uninstalled and updated it and it still skips, so for now im using windows media player to listen to songs on my computer and just itunes to update my ipod. I played a movie before in windows media and it was fine but in divx it was a little screwy

maybe try rolling back the drivers?

its not skipping as much but it still is, the only one i could roll back was the audio driver. The video said theres no backup files. And i cant roll back the audio twice, the second time i tried it, the window crashed and it said those "report this" message about kernel and drwatson

Well, I am at a complete loss. Hopefully someone will come in and be like "wow you did ALL that when you just had to do THIs???".

Wait a second... I just realised that how the heck could I help you if I can't help myself. The same exact thing happens to me... crap...