Also, K2, if he has SDRAM, he's probably not gonna have a mobo that use RDRAM (unless it's some funky i820 board from someone I haven't heard of), and not too many DDR boards come with SDR SDRAM slots.
Rambutt and DDR are faster than SDR SDRAM, BUT that doesn't have to do with stability. You can pick up crummy RDRAM or DDR just like plain jane SDR SDRAM.
I've used Win2k and while WinXP is definitely geared toward the average joe, it doesn't necessarily suck. Gaming it's great, but I'm not so sure it's better for the server setting--yet.
There is static RAM aka SRAM in your PC, but it's only on the CPU as L1, L2, etc. caches.