Hi Dave,
Everyone here started somewhere including myself.I am sure that as long as you are trying to learn, not just have someone do it for you, many people here will help.
1. The .xml file in in the Mach3 folder, ie; C:\Mach3. It is called by the name of your profile. The default mill file is Mach3mill.xml. Yours is that if you haven't setup a different name. It could be nicelookinghomemadeMill.xml if that is what you called yours. You will need to post it as a unused name so if it is Mach3Mil.xml, which has been used before, you will need to rename it to something else.
2. When you input the M03 s120 into the MDI box and hit enter you should get the blinking light. You will only get the RPM readout if you have rpm feedback. When you put anything into the MDI or a DRO for that matter you need to hit the enter key for it to stick.
3. Lets get the xm lposted and then we can work on the rest of the stuff.
Mike