HELP please stuttering issue

Please help me, this is an urgent problem because I have a video project due tomarrow and I can finish the editing.

Anyway, my computer started stuttering all of a sudden yesterday after it was turned on. I have no clue how it started, but basically audio and video are almost unusable in this condition. Using youtube is like playing a video in some sort of disturbing stop motion, and using adobe premiere to edit is even worse. anyway in attempts to fix it I have run AVG, Spybot, CCleaner, Adaware, Ad-Watch and I even updated my video and sound drivers just in case (I didn't uninstall then reinstall, simply used the nVidia update right off the site.) Anyway the problem hasn't been solved. In regards to the performance under the task manager, the CPU usage stays between 1-8% when semi-idle(since I'm using the internet)the memory usage maintains a level of about 532000/2096428.

System: Windows XP home
Intel Dual Core 2.2Ghz
2 gigs of Ram
Abit motherboard
GeForce 8600 GT 512mb
120g WD HDDparallel
320g WD HDDserial

if you need any other infomation to help me please don't hesitatate to ask, I'll just have to look harder to find it.
please help, and thank you.

this applies to videogames because they severely stutter too, but are still usable....but they're not important to me now at this second.

Have you tried a system restore back to when your speeds were fine?

Also, is your hard-drive thrashing (is it being accessed constantly or near constantly?)

I assume I solved this problem....wow my computer is old...