Hi there A VISTA PE system has been done for a while now A similar method *should* work for W7 provided you can get the WAIK for W7 (or it might work from the W7 install DVD).
The following is a link that explains Windows PE 3.0 in greater detail for those wondering what the heck Windows PE even is.. Believe it or not, there are quite a few people who think it is some new version of Windows 7.. This link is to clarify that it is in fact NOT some new version of Windows 7...