I have been at a loss for quite some time to explain the frequent, daily reboots of my nice, new server. I bought the best equipment I could and still the machine seemed flaky. It was even more unstable with the beta version of Exchange 2007, but I think that was caused by much more frequent usage.
On a whim, I decided to look for new drivers and BIOS for my system. I found them. I found a BIOS update for the motherboard, a BIOS update for the RAID card and a new driver for the RAID card. I flahed them both and installed the new driver.
Voila! The server, which used to reboot daily [or more!] has been up and solid for over three days straight. The problem seems to be solved just in time for me to upgrade the equipment with a second processor and 2GB more of RAM… Fun!