I'lll one up you guys
I have pictures of XP SP0 running on an old crappy HP Vectra XA5 -- Pentium 90mhz processor (60mhz FSB for the win! No MMX on these either...), 64mb of ram and a 4Gb drive. It actually served as a headless firewall, router and telnet host for my miniature home network way back in the day when home internet routers were still stupidly expensive.
It had two 100mbit nics (yeah right, like you'd EVER saturate those on the whopping 30mhz PCI bus) and a Matrox video card (if you didn't have a VGA card, it wouldn't post
) NO keyboard, no mouse, no monitor -- everything was done via RDP.
The screenshot I had was a network uptime of like 390 days
It took forever to boot, but once it was up, it did great!