...can you do a clean install with an upgrade version with out formating the hd?
No...hense the adjective "clean". Doing a clean install is installing the OS on a perfectly clean HDD and nothing else on it. It is much perfered.
I'd really move whatever you want to save over to another drive, or burn them off on CD's or whatever and do a clean install....that is if you really really want to save something.
However, to be honost, there's nothing better than not only doing a clean install of the OS but to do clean installs of your programs as well. And that's what I would really urge you to do.
If you do this, then all you do is put in the XP disk and install it. I can't remember if you HAVE to fdisk before this step or not because I still fdisk using a floppy drive on older drives with stuff on them. I belive that you can choose a total new install from the XP disk, then it formats the entire disk to NTFS format. But prior to all that, it should see your prior install of windows and doesn't ask to "see" your old disk.