iPhoDroid is probably a really waited application for lots of iPhone users. It allows now the installation of Android on your iPhone, under Windows operating systems. However, it is not clear if it is compatible with any Windows or with any iPhone, but it should work over XP and Vista (both 32 and 64-bit platforms), and for the 3G iPhone (from what I've seen on YouTube).
I don't know if it works with Windows 7 or not, or for the other models of iPhone, but as long as you haven't found anyway a confirmation that it works with your OS and with your iPhone, I don't recommend you trying this. Moreover, you're doing everything on your own responsibility, so if something goes wrong, you might have to restore your device.
Direct download for official site (please notify me if the link becomes unavailable): iPhoDroid download.