Your Mach3 settings are contained in <your profile> .xml file. If you have any special screen features then they are saved in you screen .set file (typically 1024.set). If you have any special Brains or Macro's then they are saved in their respective folders. Your Mach3 license is saved as Mach1Lic.dat. All the above are in the Mach3 folder.
The safe bet is to make a secure backup of the complete Mach3 folder then, if necessary, copy the relevant files / folders to your new installation.
Tweakie.