|"I think that PIII can only support 256mb chips and have 2 slots, so 512mb would be the limit."|
The P3's L2 can cache up to 64GB of memory. It's the motherboard that determines how much memory may be installed, and in what configuration.
The common i810/815 chipsets only support up to 512MB. The older i440BX on a board with 4 slots will support up to 1GB (256x4 low density). Newer VIA Pentium III chipsets support up to 2GB (512x4 SDRAM) or 4GB (1GBx4 DDR SDRAM).
Pentium M oc'ed to 2.82GHz, 667FSB, 2MB L2
3GB of DDR-800 @ 667MHz
Modified PowerMac G4 'Quicksilver' case
HDMI to homebuilt 1080p projector