I also am dual booting, although I have Vista on its own partition. I didn't test deleting any system files, but I have no problem deleting other (ex. program files) on that partition. So while I'm not sure, I doubt that your Vista install alone has caused your problem. Sorry, I realize that's not exactly a helpful answer, but it may point you in the right direction. If you end up at a dead end, you should be able to salvage the non-vista files from within Vista by resizing your partition on the fly, creating a new partition, and moving your non-Vista files there so that you can delete the Vista partition. I'm really curious why as to why you didn't create a second partition in the first place. Not being critical, just curious.