I did a search to install xcode on Windows (particularly Windows 7 in this case) and I found a website that tells you how you can do it. From the comments, it seems like it works.
I am currently in the process of doing this. It took me 3 hours to download Snow Leopard, and don't feel like messing with it now. So i can't guarantee if this will work, but if it does, it will be cool. It does require you to have at least 6GB (I think) of hard drive space. You also have to have a computer capable of PC Virtualization.
Like I said, I haven't done it and not sure if it will work. It will also take you hours (depending on your Internet connection). If anyone else has done this let me know how it works. I'll try it tomorrow.
Here is the link:
http://ipodtoucher55.blogspot.com/2010/12/installing-ios-sdk-and-xcode-on-windows.html