New Computer.. Low Performance...

I have spent about 5000$ on my new computer.

I have 4gb DDR2 PC 6200 or something RAM

Intel Quad-Core 6700 CPU. (i think)

500gb 7200rpm 16mb Cache Harddrive

100gb 15000rpm harddrive

4gb RAM Drive

ASUS Nforce 680i motherboard

Antec 500 watt power supply

8800GTS SLI 384mb

Creative X-FI Elite or w/e edition

With latest drivers. I am running Windows XP 64-bit edition.

I have very low performance matched with my old one. I have no running background programs. CAN ANYONE HELP ME PLEASE?

for instance, when I play Day of Defeat Source, I put 6x Antialiasing, everything upped (also using CVARS in autoexec.cfg) basically i have everything turned on that Source engine can offer. (unless Source has subsurface scattering and such). Resolution is 1680x1050. I only get 30-40 fps constant. I do not have it capped.

This is a serious problem can anyone help me please? Thank you.
Check the apps that are running in your Task Manager and see if you have alot of resources
tied up in somthing else, like Antivirus scan or spyware scan. They will really slow you down.

Oops, saw your note too late!
perhaps running at max in the midst of battle you get low frame rates...try an empty game with the same settings and see what you get...if you dont get anymore frames in a game with 1 person than with 32...then chances are its a software problem somewhere...but if you are getting more frames in that single person game...then maybe running at max it too much...try lowering your settings and see if you get better least you know if lowering your settings fixes the problem...then its not software related...currently i had somewhat of the same issue running source on my computer...i run the newest kernel release of freeBSD and the brand new X server...and had not changed my settings once on source...the second i updated the kernel...i was getting crappy frame rates...checks out that when i updated the kernel it sent my old nvidia drivers haywire...and when i was lowering the graphics settings it didnt change the frame rate at all...i was at the bare minimum getting 20fps...and at a decent setting getting the same...hope this helps you deduce your problem... happy hunting!
You may also check your cooling on your new rig. My cuz ordered a new comp from cyberpower and they didn't hook everything up. So open the case and make sure all fans are running and nothing is blocking them. Also 500 watt power supply seems a little low powered for a rig like you have. I have a 500 watt power supply for my 7950 gt vid card with 3 empty pci slots. So the more stuff in your rig the more power you need. Run 3d mark see what score you get then check some of the things mentioned here and above and run 3d mark again. Good luck buddy.
About 2 months ago, a steam update really made my game lag badly when I connected to my hlds server on the same machine. It hadn't previously done that, but the solution was to set the steam.exe priority to high in the task manager.

I don't know if it might help or not since I only have a single core cpu, but it's worth a try I guess on your hl2.exe.
Sorry to say, but a 500w power supply wont cut it. Atm, your graphics card is eating away at your computer. And is about to fry your motherboard, and leave your powersupply powerless.

I would recomend a 600+ watt supply, at very least
As far as power supplies go, generally most power supplies will do. Most video cards, even those dual processor video cards as well as running them in SLI do not require as much as power as you would normally think. They will rarely use more than perhaps 150 - 200 watts each. Motherboard's, processors, ram, hard drives, and chip sets generally wont total more than 80 watts under full load. The rating on the power supplies is max output, so figure your average usage under hard gaming will perhaps reaching 400 watts. That is probably a lot to begin with, and generally when you actually run out of power your system will crash. Power supplies are not equipped with a rheostat, so they will not continue to draw power when you have reached their max limit. So your system will most likely crash if you infringe upon a peripheral that is directly in use by the system. So if your video cards are running out of power you will lose video first, rather than performance. Since there is no rheostat, they will just shutdown. At least first rule out a software problem, then move onto the hardware. That is most likely the problem at hand.
k lol i returned the powersupply i bought a 850 watt SLI powersupply. it still does the same thing. I have updated every single thing i can on this computer. It is only Steam. Call of Duty 2, Quake 4, FEAR runs at 60fps constant. ehhhh
Hmm, if you go to the official DOD forums you'll see a lot of people in your situation. I'd be annoyed if I was you.