Impossible Stuttering Problem

So I just built my new computer. New everything.

ga-p35-ds3l motherboard
e2160 penitum processor oc'ed to 3.0ghz
8800gt 512mb video card with latest drivers
2gb of stable 6400 ram
500gb hd
etc

My problem is that my graphics stutter. It runs smooth, then jerks, then runs smooth, then jerks, etc. It happens whether I'm running 3Dmark or if I'm just dragging a window around the screen. The most strenuous and the easiest tasks all stutter. 3DMark06 will show 80fps, then drop to 25 for split seconds. It happens at regular intervals.

So last night I found out that I had my memory in the wrong slots. I have 4 slots, 2 for each channel. I had both of my DDR2 memory in the same channel, which made them not work in Dual Channel mode. I swapped one stick to the other channel, and voila, everything worked.

Then I restarted after installing stuff and running tests, and Windows told me I had recovered from a serious error. Sigh. The skipping came back. My mouse is jumping, my framerates are dropping then coming back at regular intervals, etc. As an added note, I ran Prime95 overnight and when I checked on it this morning, I did not see any test results. Nothing was running. I think it rebooted.

Is this bad memory? Is this anything anyone can help me understand? Does it have to do with my overclock? Voltage issues? My memory timings are are 5-4-4-10 with 2.1v. My CPU runs full load at 3ghz in Prime95 at 45c. I don't know what other info to give or who else to ask, so any help is appreciated.

OC a little less/cool a little better/up the voltage a little. Once you find something stable, don't forget to take it down a notch AGAIN ... especially if you do your stability testing overnight, when it's significantly cooler (the trick is to just not do this - if you want to test your computer's stability, you HAVE to test it at the hottest point of the day, as well as over a long period of time.).

Also, try rolling back a version of drivers. I can't comment on the current state of vista drivers from nvidia, but when I bought my last notebook (with and nvidia 7800gs, I believe ... and vista) the drivers for vista were consistently so bad, with the exact problem you describe (every 10 or so seconds it would go from smooth framerates to pathetic framerates, around 10fps, then shoot back up after about a second), that I ended up returning the entire notebook to costco for a refund (I installed xp first to isolate the problem - that solved it, but I wasn't going to pay the microsoft tax on an os that I wasn't even going to use).

so, once you actually have done more than a half-assed job of OCing your computer (you sound like a novice; do some reading, at the very least follow a guide carefully), then you should start to look into driver issues. If you don't get a guide, at least ensure that you stress test your computer at least 6 hours (I do 12) and make sure those 6 hours include 2 pm (often the hotest part of the day is just after noon, right?). Then lower your OC by a bit (eg I tested my undervolted c2d at an oc of 1ghz ... from 1.8 to 2.8 ... then I clocked it down to 2.7 using the same voltage. Then I tested it again.