Thanks usasma, I think what the whole thing boils down to is simply the fact that I have a 32-bit OS and it won't read all 4 GB of RAM. That's about the only consistent statement I've seen in my research. You're right that since I have a newer chipset, the extra RAM won't hurt my computer. I went to eVGA's website and was able to find a FAQ for exactly my problem (although the issue was with Vista 32-bit, not XP Home) and I'm guessing that my very expensive motherboard simply just doesn't support memory mapping and I'm forced to upgrade to a 64-bit OS if I want all 4 GB of my RAM recognized, which I plan to do eventually anyway. I'm just leery of all the problems I've been hearing about Vista, though and am afraid my rig will implode.
As for updating my BIOS, I did read the release notes and didn't see anything regarding memory mapping, but figured it couldn't hurt to update anyway since the release was just last month.
I understand some of the language regarding memory and bits, just enough to draw a theoretical and logical conclusion that satisfies my furrowed brow. I'm no programmer or anything, I'm just a gamer who wants a high-end rig to play Oblivion, COD4, Crysis, etc. with most, if not all, the eye candy!
I consider this matter closed, thanks for all the input and help guys.