For the most part, after weeks of fighting with this, I figured out some fixes for some of the problems.
First of all, get X-Setup by Xteq, TweakXP, or some other application. Within your tweaking app, there should be an option (somewhere) related to crashing where you can disable "automatically rebooting on hard crash" or something like that. In any case, the outcome should be that you get a bluescreen and a memory dump instead of automatically rebooting. On that bluescreen, you should get an error message like the following:
Here are the three I used to get, randomly, and how I fixed them:
UNEXPECTED_KERNEL_MODE_TRAP: This one was sneaky. Even though I had completely disabled my personal firewall and antivirus (Sygate Personal Firewall Pro and Avast! Home Edition), it still would give me this error. I found out that most of these firewalls/av software, even when disabled, will still run in some form in the background. I uninstalled both applications, and I no longer get this error (however, I don't advise you to be fully unprotected, especially if you're on broadband...I plugged in my linux box and set it up as a firewall, and got a less obtrusive virus scanner). I know the technical reasons for this, involving win32 system traps used by firewall apps to block unauthorized apps, but I won't get into it.
DRIVER_IRQL_NOT_LESS_OR_EQUAL: This one was kind of a "duh" for me when I figured it out...ASUS motherboards share an IRQ between the AGP port and the first or second PCI slot. I fixed this one by moving my IDE controller card down to the third PCI slot, and this error stopped.
I had a third error that I saw right off was a crash in the video card driver, nv4_disp.dll. I fixed that one, actually, by "downgrading" my video driver (I installed some older Omega drivers for nVIDIA cards manually through the system hardware manager, and I just installed the older ones right over the new ones). That made that error go away (I can't remember the actual error message though, I seem to have lost the slip of paper I wrote it down on, but I clearly recall that the name of the video card driver was on the bluescreen and that the crash was in that file).
I also saw an error in uhcd.sys, which is related to USB. You may need to uninstall the drivers for one of your USB devices if you get this error.
Anyway, after fixing all this stuff, I still get the occasional crash to desktop. But it's very few and far between, so it's acceptable. I'll figure those out eventually, they're probably a side effect of downgrading my graphics card or something to do with my sound card, ASUS motherboard drivers, or something stupid like that.
Anyway, thanks for the suggestions all, and for those having problems...stick with it, this game is worth it for the hassles (although, I'm pretty sure I'm not going to get too many of those hours back, but at least I know my system's more stable now than it was!)