When you had it on Win7 did you have parallel port driver installed.? . . . Mach3 Parallel port driver won't work with Win7 64bit so if you didn't install it but you have with XP then this may be the problem because it's looking for spinlde feed back.? Also XP 64bit won't work with PP driver.

Try the Mach3 forum asking the Lathe Lads, Hood will probably know.