Odd lag problem

I'm getting a strange lag problem with a couple of my games. The last time I saw a problem similar to this is when I had a failing power supply (the problem persisted out of games however.) Right now it only seems to be happening in Left 4 Dead and Mass Effect. Here are a couple short videos I took to show the lag a bit better than I can describe.

(Lags) Mass Effect
(Lags) Left 4 Dead
(No lag) Dead Space
(No lag) World of Warcaft
(No lag) Counter-Strike: Source

My rig isn't amazing, but it gets the job done.
Specs:
AMD Opteron 180 dual core 2.5Ghz
Nvidia GeForce 8800GT
3gb ram
Windows Server 2008 x64

try turning down anti aliasing or texture quality

Damn.. I've got a 350 watt PSU for my video card and 1 hard drive and another 550 watt for the rest of the system and it is still doing it... Think that rules out any PSU inadequacies.

you use 2 seperate PSU's?
or is it one of those modular wotsits?

Ok well it doesnt necessarily rule out the power issue. 8800 GTs like ampage man, and the 12v rail supplies the card. your 12v needs to have 24A to be adequete, otherwise it will be jumpy under load.
Can you link some specs for the 2 PSU's ?
I can tell you with 99.9% certainty that the 350w PSU belongs in the bin

check this one out for a nice PSU...$50 after MIR.
Wouldnt SLI on it though if you are planning to...would have to look more in the PCP&C 650 Range.