Jeff - I was going to say that as well - Windows needs nearly all the 256 mbyte for itself, leaving precious little for Mach. When Windows needs some, it just grabs it (it gives it back when it is finished). Get a 500 Mbyte memory card, either on its own, or with your 256 Mbyte already and you will be a lot better.
I say 500 Mbyte, becasue they seem to be quite cheap at the moment. 1 Gig would be even better.