As far as I know, it shouldn't erase the files unless you switch file system formats on your hard drive (e.g. from NTFS to FAT32 or visa versa). Don't reformat your drive and you should be fine (I admit, I've never attempted this feat, since Vista SP1 was a turd in the punch bowl, and XP was a much more solid system to work with). Again, if it's anything like previous Windows systems, it'll work just fine!