Here's the short version. If anyone has an inkling on what might be the issue, I'm happy to provide more details about hardware/software, etc.
I'm running Windows 7 Pro 64 with 4gb of RAM installed. However, my BIOS is only reporting 2gb. Windows Task Manager shows 2gb available, and Resource Monitor shows 2gb total, 3gb installed.
Where it gets interesting, though is: everything else (CPU-Z, AMD Overdrive, etc.) shows that they DO IN FACT see the two sticks of 2gb ram. I've done all the basic stuff (memtest shows both sticks as functional, "maximum memory" is not checked in msconfig) but for the life of me, I can't get my BIOS (and, by extension, Windows 7) to recognize the second stick of RAM.
My motherboard is a Gigabyte GA-880GM-D2H. Again, I can provide any other technical information that might be helpful.