Hi Patio! Long time no see!
I saw nothing in the OP's post about installing XP. Eh?
All I can see is him asking if you can format C: in windows
and of course the answer is NO, windows will not re-format the OS drive,
on which it resides, which should be C:.
If that's not what he meant, I wish he'd come back and explain in more detail.
The devil is in the details! Natch!