Restarting problems during installation, and afterwards

OK, I'm almost bald from pulling my hair out. Here is the situation. I am installing WIN98 SE on a brand new system. When the installation gets to the point where it is setting up the control panel, specifically, the system configuration, the computer will restart all on it's own. It will continue to do this several times until Windows finally does install. However, when running applications after installation, the system will continue to restart all on it's own.
I have disabled power management in the bios. I have swapped out RAM, same problem. I have swapped out the hard drive, same problem. The system is not overheating, and the PSU is working fine. I am beginning to believe that it has to be the motherboard, as I have run out of other ideas.
Here is the set-up I am installing and running with:
Gigabyte GA-7IXE Slot-A Mobo
AMD Athlon 900MHZ T-Bird (Slot A)
256MB PC133 SDRAM
20GB Western Digital HD
16X DVD ROM
NVIDIA Ge-Force 2 32MB AGP
300W PSU

ANY ideas or comments would be greatly appreciated! Thank You!

A few things that spring to mind:

Faulty IDE data cable.

Make sure Spread Spectrum is disabled in BIOS.

Change to Standard PCI VGA driver & borrow bog standard PCI video card. If OK then suspect video card or m/board AGP.

Corrupted 98SE CD?

If all other possibilities seem eliminated, then suspect motherboard.

I ran into something like this last weekend when I was doing an upgrade on a friends sys. What was actually causing the system to reboot was a driver issue. Every time the modem was accessed through DUN, hyper terminal, or in modem diagnostics the system would reboot itself, updated the driver and haven't had a problem since.. One thing I would suggest is just try to make sure everything has updated drivers installed..