Okay, first of all, why are you (the OP) running a three-and-a-half-year-old version of Ubuntu that is 7 versions out of date? If you want LTS, get 10.04, *not* 8.04. And even with 10.04, there is still another LTS version coming next April that will have all the up-to-date things that newer versions of Ubuntu currently have.
Secondly, why in the heck would you want to delete the "unwanted Ubuntu 8.04 OS files" anyway? If you dislike Ubuntu 8.04 that bad, delete its partition (or, if it takes up the entire hard drive, just format the drive and reinstall Windows), but don't come crying to me if you get a GRUB Error 22...