** Note: make sure you have the proper licenses/product keys for BOTH Windows 7, lest ye run afoul of the law. **
The only way to eat your cake and to have your cake:
Do at least one if not two full images onto at least one if not two external hard-drives of your OS and stuff partition as it is right now.
Then, after verifying the integrity of your backups [reading test], remove all of your stuff from Windows OS, for example, pretend you have Cyberlinks galore, Lebre or Open Office galore. Uninstall via Revo Uninstaller Pro [if you have any 64-bit software] all of your galore nonWindows OS stuff.
Be careful! Do not remove drivers or software that works with your Windows concerning video, sound, network, and such. [Or your Windows could end up crying like Tammye Faye at a garage sale.]
Make at least one if not two full images of your now-thin Windows OS partition onto at least one if not two ext HDs.
Create your Virtual Reality/Virtual Machine that will house windows 7. You MIGHT be able to restore the nowThin W7 into the VM, or, you will be forced to do a fresh install within this VM.
You can restore your normal full house back onto the regular internal hard-drive from the full image you made at the beginning.
** Note: make sure you have the proper licenses/product keys for BOTH Windows 7, lest ye run afoul of the law. **