Check your hardware.... Unplug everything you're not actively using. Most of the crashes I see are caused by hardware drivers. Something eating RAM usually just causes the computer to slow down.
If you use a lot of USB hardware, you can clean out the old stuff and reclaim some COM ports by typing the following two lines in a command prompt:
Code:
set devmgr_show_nonpresent_devices=1
start devmgmt.msc
That'll start device manager; then under the "View" menu, choose "Show hidden devices". Expand Ports, USB devices, etc, and Uninstall the stuff you won't use anymore. I go through a lot of USB-Serial adapters at work, I got up to COM80-something before I found that trick.
What happens or causes the crash? Does it always happen when you start some program, or after the computer's been on for so long, etc? Usually they happen for a reason, and once you know the reason it's pretty easy to pin down the cause.