Mach2 was the predecessor to Mach3. The same license should work, though. Just copy the license to someplace safe, then download Mach3 from Machsupport.com, install it, and put the license file in the main Mach3 folder.
If you're getting someone else to write G-code for you, make sure they use a post-processor that's compatible with Mach3. It's Fanuc-based, so if there's no Mach3 post, try a Fanuc one. You also should have them tell you where the origin is; it's possible to zero the Xand Y axes in the middle of the part or off in a corner; the Z can be zeroed to the top of your stock or to the bed of the mill, but it's important to know this stuff before running the program.
There isn't really a Taig manual as such, although there's extensive documentation for Mach3 and instructions for setting up the Taig mills. But I've got a fair amount of experience with them, so if you have any questions about these mills, feel free to ask.
Andrew Werby
www.computersculpture.com