Can i install xp pro over an unfinished home installation?

The problem im having is that i tried to install xp home on two computers but i realised i didnt have a key for it and i have the genuine disk. Later i found i have the xp pro disk with the serial numbers for it. Well when i turn on both comps both show put the xp home disk and the serial key. Can i install the xp pro when the unfinished home hasnt been installed.

P.S. one comp is a laptop the other a desktop. I have tried booting off the cd it wont work. Any help is appreciated.