Try turning off the onboard video in Task Manager, and see if Mach 3 manages any better then. It will give you some idea.
With 3 Ghz of memory (which is what I assume you are saying) then 10 Mbyte should be no problem. If it is a complex file, it may be just that Mach3 was spending too much time worrying about the job instead of just getting on with it.