How to migrate with windows OS but no other programs

I want to move my windows 7 operating system over to my new mac without buying a new copy. I have tons of programs...including stuff that slows the thing down that I don't want to transfer.

Parallels tech support says I can migrate it over but doesn't seem to know if there is a way to do that without bringing over all the crap. Can I bring it over, then format back to the OS? or maybe bring it over and upgrade to windows 8 which has an option to upgrade to clean OS?

Any ideas or experience?

thanks!!