When you run the uninstall, one of the options ought to be "Program Files Only" If you select this, the directory structure should be left in place., along with any locally create data type files. Delete the MSDE database as well
IF you don't or can't delete the tape drive(s) from the v8 install. They will still show up, as disabled, in the new install, and you will have to do some MSDE diving to remove them.