My .02
XP by itself is not very happy with 256 sdram
My wife's PIII 1.0 with 256 and it shares 11 with onboard video is a slug.
My computer is home built, 1.2 AMD Duron, 512 sdram, WD 7200rpm HDD 8mb cache.
WinSPMBT plays just fine as did DOS versions.
Overall I am impressed too. The only issue that I have encountered is the intermittent sound, which is really obvious during an artillery bombardment. I actually like the 480 x 640 resolution the best. The icons are bigger so I can see them better. I tried the 600 x 800 and I just can't get used to it. One feature that I like in SPWW2 and SPMBT versus SPWAW was the bigger icons. I guess it is due to the resolution of the games.
I hope that the sound issues are resolved soon.