i would boot into A: promt using a boot disk from click here then use the format c: command which will erase windows xp. Then install windows 98SE - btw this is the full version of windows 98 isn't it? Then just use the upgrade disk.
Like this if you have not got a Win98 Floppy start disc go click here and download a OEM Win98se boot disc. put a floppy disc in computer and double click the download it will create a boot disc for you. Then restart the Comp with the Boot Disc, and at the A:\> prompt type FORMAT C: like this
A:\>FORMAT C: press enter just then press Y for yes when it asks when it gets to the end it will ask for a volume name just ignore and press enter it will return you to the A:\> with a clean drive. Restart your computer with the floppy disc and choose START WITH CD-ROM SUPPORT put your Win98 Disc in the comp. After it as done loading the Ram Drive etc. it will return you to A:\>
now this is the tricky part, If your CD-ROM was D:\ it will now be E:\ no matter what the letter was it will move up by one letter.
Type the CD-ROM letter i.e. if it was D:\ type E: and press enter then type at E:\SETUP like this
E:\SETUP press enter and follow the instructions on screen from there, Have your Win98 Reg KEY ready on the Win98 Book
Rennaissance My understanding is that an upgrade disk is the full installation, at a cheaper price than the full retail version, to persuade you to upgrade . At some point in the installation you have to confirm, by running the original OS CD, that you are actually upgrading.
As long as you can do that, you can run a 'clean'install with an upgrade disk.