Hi Shoupie and thanks for your stress test results.
The CS:S Stress Test tests *only* the GPU and this was required to see if your X1900 is performing properly. By comparison, an X700 can usually only muster about 60-70fps in the Video Stress Test. So your X1900 is actually installed and functioning properly with it's 117fps VST result.
On your performance- playing CS:S online is different from the stress test. For example, you could bolt an X1900 into a Celeron 2.0ghz system and still get 117gfps in the stress test, but be running in the teens online (10-15 fps).
On your upgrade, realize things become drastically different between an x700 and x1900 as the new card has a ton more features (FP blends for HDR, Shader Model 3.0, etc.etc.) Source Engine is designed to fully use the features of the installed videocard, which while 80-90% of the work is done by the videocard, they carry along more CPU work to format/process these new features. So in many cases, where cpu-bound to start, upgrading to a higher-calibre videocard will often times see a DECREASE in performance, but with substantially nicer looking visuals. Water shaders, HDR and other effects will look nicer, but they take with them more CPU toll which was your problem even with the X700.
There is obviously something about your setup that is crippling your P4 as it's not able to muster enough power to drive the uncorked video card now in Source Engine. While even Core 2 Duo's can struggle with some of Valve's network code (it's very cpu intensive for little reason in a variety of conditions), what's important is to tune/fix your cpu and memory performance to get more out of your X1900.. which in the case of playing Source at 1280x1024, you're likely only getting 50% of what the card can handle due to your CPU not keeping up it's end of the deal.
The nice thing here is you can raise resolution and lop-on more AA and AF without altering your performance much. It's basically taking up the "slack" that your videocard is running mostly idle due to cpu-bottlenecks.
I'd recommend the next step to be downloading SiSoft Sandra and run it's arith tests and memory bandwidth tests. It's a free download at
www.guru3d.com downloads section. Run these two tests and report your findings. I'd hope memory bandwidth is >4500mb/s in all cases else we have conditions that will cause a P4 to perform like the above aforementioned Celeron!
Cheers