Have you run the setup files from off the CD ?
It will install Mach in metric mode as all the screws etc are all metric.
This makes no difference to uses who want to work in inches as the G20 code at the start of a program will tell it to use imperial.
For anyone want to work in all imperial by default go into config > general config and in the initialisation line type in G20 and change the F125.0 to 6.0
This makes Mach start up in imperial mode with a feed of 6" per minute for jogging etc.
Any feed rates in a program will over ride these startup setting but the default settings, G20 F6.0 etc will be there next time by default.