assuming that you have FAT32:
go to this site and get your self a boot disk
windows98Se OEM)
http://www.bootdisk.com/bootdisk.htm
save the file on your hard drive and run it to make a boot disk.
Insert that into your computer and do to BIOS and change the Boot Option to start from A: drive first /save and exit/ reboot
your system should boot with the floppy, so on the command prompt create a new directory call it "saved", then copy evey thing that you want to save in that directory.
at the prompt type in c:\deltree . ,, at this point your computer will ask you if you are sure that you want to delete the file,,,, press "Y" for yes to every thing except the "saved" dirctory . when all the unwanted files are deleted, you can install the new operating system,, WALA,, there are other way of doing it too,,, but let's stick with something simple
[this will work like charm if you have FTA32]
let me know how it works out for you
cheers