CS:Source glitchy/jittering/stutter problem! help asap!

Hello, I have gone through hell for the last 2 months or so, I have been playing this game since April of 07 and nothing quite like this has ever crossed paths with my pc and counter strike source. Each time I am in a server I am always glitching and lagging all over the place, I had to take a stop to competetive play because of this, this is unbearable and I need a fast solution or idea on how to fix this ASAP. My computer specs are as follows, I just got this setup last month, and before I got this setup I had a ver yvery bad pc the one in which i started playing since apri l07 with and noticed the glitchy, jittering BS that has detered my competetive play. My specs are as follows:

OS: Microsoft Xp Professional
Processor: AMD Athlon(tm) 64 x2 Dual Core Processor 4200+, MMx, 3D now (2CPus)
Ram: 2048 Ram
Direct X 9.0
Nvidia GeForce 7900 GT/GTO 256.0 MB

I have tried all kinds of crap man, from hotfix, amd x2 patch, amd optimizer, amd driver, uninstalling /reinstalling, affinity set, all types of retarded game configs, im at witts end, I need help fast, Please help

Thanks for your time

( Ihave already read the 10step sticky )