Your hardware sounds muscular enough, but I understand your distaste for the cost of an upgrade to XP.

Did you start the installation from scratch, or did you do one of those "repair the system" installations? If a virgin installation, did you tell the installer to reformat the hard drive first?

I'm wondering now if the boot sector on your hard drive is screwed up. Starting over, and telling the installer to reformat the drive, may cure a bad boot sector. Or you might try another drive if you have one around or can get one from one of the neighborhood packrats.

You can tell I'm getting to the desperation maneuvers now. The situation needs something radical.