Although I don't know for sure if you can successfully install Win 7 onto a 4GB HDD, I don't really think it would work very well if you did actually manage to pull it off..

I say this simply because I know with Vista if I created a partition any less than 20GB's it seemed to run like crap.. It's not that it wouldn't run it just didn't run very well.. but of course that could have been because of what I was doing on the comp too.. Video editing and what not requires alot of disc space so that no doubt was most of the reason...
But like I said, I don't know for sure if you could do what your proposing or not.. I think I may give it a try though now that you bring it up.. I'm curious to see for myself.. I've got an old 10GB HDD kickin around here somewhere I could try it on...
Sorry I couldn't be of more help...
