Long, detailed. Thanking everyone beforehand :D Okay.
Assembled my system early this year, circa March. Ran fine until I got BSOD last week, something mentioning IRQ. I turn the PC off, back on, and get the speaker error System failed due to overclocking. I call the only person that had ever used my PC recently, and found out my cousin had it overclocked 30 percent since a few months ago (to 3.6Ghz)
I bought a new similar mobo, still didn't work. Took out the CMOS battery, replaced, same problem. I take out one stick of RAM and now it works - I put the stick back in, it won't work. Problem is, I don't have a detailed record of what kind of stick I bought, all the label says is
Komusa-PC3200 512MB DDR. Each stick (four total) has copper heatsink-type plating, or at least something resembling it if not plating. Can I buy another single stick? Does anyone know of a site that sells the exact kind I'm referring to? :)
Secondly, I have my same ASUS P4C800 deluxe motherboard. The specs on the box say Multi-RAID for ATA133 & serial ata.
I have this HD right now :
http://seagate.com/cda/products/discsales/marketing/detail/0,1081,597,00.html
ST3200822A, Barracuda 7200.7 Plus-200GB Ultra ATA/100, 7200 RPM, 8.5 ms avg.
Could I buy another identical HD, set it as a slave, and have it work? There's another empty connector at the end of the cable the current HD is on, and I have a 430 watt power supply.
Thank you. :) [again.]
Feel free to AIM or email me if you have knowledge on this subject.

First, downlaod and run Everest home edition. This free utility should give the the exact memory module info. Next, if you need additional storage space it sounds as though you have numerous options available. You can add an additional HD. You don't nned an identical HD unless you want to use a RAID array. I think your RAID capabilities with that board need SATA harddrives.

Last time I tried to use two different HDs they wouldn't work, my cousin, who's in the field of computers, told me it had to be the same brand name or they wouldn't work together..
So, even though this Seagate is an Ultra ATA, I could get a Serial ATA HD from Tigerdirect.com for instance, made by a different company, and I could use that also? I intend for large file storage and backup for the HD..

You may have misunderstood your cousin. If you want to make a RAID array then the drives should be identical. For general computing it isn't necessary. I have machines with 3 different sizes, brands and ATA ratings. You have SATA onboard. I suggest you invest in a SATA drive for forward compatibility.

Thank you very much! :)