Windows XP
ASUS A8N SLI-Premium
AMD Athlon 64
400G hardrive
2G ram
Raedon HD4890
700W Kingswin PSU

Rig is about 4 years old now, I just added the PSU and video card about a month ago.

I woke up three days ago with the Mobo beeping every couple of minutes. Initially, thought it was the smoke alarm, but it seems like the computer was just rebooting itself in an infinite loop...

I can turn it on, POST completes without a problem, then I get the "Windows did not successfully shutdown...." with the typical options, boot in safe mode, safe mode with networking, safe mode with command prompt, last known good config, or boot normally. No matter what option is selected, the Windows splash screen appears for half a second, and then the system just restarts itself.

What I've tried so far:
Clearing CMOS
Removing mobo battery
Removing non-essential components
Removing USB peripherals/devices

I assume my next step is to boot from a CD and reformat the hard drive. However, seeing as how I'm at college and don't have a handy windows CD, I figured I would ask if there was anything I could do in the mean time...

Any help is appreciated.

The first part of the problem is the repeated restarts after shutdown. If you could stop those, you could get error messages that might be useful in diagnosing the problem. Try this:

Start -> Control Panel -> System -> System Properties -> Advanced -> Startup and Recovery
-> Settings -> System Failure -> then Uncheck Automatic Restart and reboot.

You might then get some code on the screen that has digits enclosed. If you cannot read them, post them to TechSpot for someone experienced in looking at a lot of them, and figgering out what they mean.

Sounds good, but I cannot boot windows to get there, and I haven't found anything similar in the BIOS...

Has every symptom of a failed hard drive, but the beeping.
The beeping on that board is typical of memory socket failure we have seen a number of times.
Have you tried booting to one memory module, then change sockets and do it again, then change memory modules and repeat the process?
... each time, carefully assuring that the memory is fully seated. Look for crud in either end of the socket as well... and clean with Dust Off or equivalent.

Well the beep comes from the mother board as the typical notification when the system is turned on successfully. Its only one beep early on in boot up.