I have run vista on a bootcamp partition( on a MBP 2006) and I did not notice a battery issue. The main issue is that microsofts aero theme requires a lot more resources than OSX aqua. So the graphics card will probably be using a bit more power in the windows partition. However, the main problem will be how you are using the machine (gaming, video editing, etc. )

Win 7 is much less resource intensive than Vista. When running vista I did not notice that the battery was drained any more significantly than when on OSX. As such, I can only imagine that the same or better can be said of Win 7...