After much shuffling around, Olympus is back in operation. Sort of. Windows XP is reinstalled, although it decided that the small partition that it sits on (previously C:) shall be called D:, with my larger partition (previously G:) called C:, and no way to change them. Oh well, I can get used to Windows residing on D:.
Less success with the router, however. The Gentoo LiveCD's (2004-1 Minimal, 2004-2 Minimal, and 2004-2 Universal) all suffered from strange reboots at various points during bootup (although always the same points). Early experiments with a Knoppix LiveCD exhibited the same behaviour. A Slackware installation CD did work, though, and later tries with Knoppix failsafe versions concluded that distros that didn't try to do much or detect much hardware tended to work, but those that did always rebooted.
I then discovered Knoppix without AGP support worked and concluded that something must've been wonky with the AGP port (earlier experiments had showed that neither RAM, HDDs, or NICs were the root of the problem, and the graphics card was PCI) and proceeded to try and install Gentoo via Knoppix. All worked swell, actually, and I managed to get partitions set up and configured nicely. Then I tried to download a stage tarball. Fired up links in all its consoley goodness and went to the FTP site, highlighted the stage 3 tarball, pressed enter to download and... the computer rebooted.
I'm currently running memtest86 again, despite that it had earlier shown nothing wrong with the RAM. Another suspected culprit is the PSU, but I have no way of verifying that. If anyone has any ideas... do comment.