I'm not too sure what effect the native OS has on the performance of WinUAE - but under XP I'd certainly recommend popping in at least another 512Mb of ram. A faster CPU (say >1.6GHz) would improve things also.
I'm using an Athlon 3200+ (2.0GHz, Barton core) with 1Gb of ram on WinXP and everything's just dandy.
:-D
