Win XP Pro Upgrade software

Got a question.
I just bought a Compaq Presario lappy and it has Win XP Home installed on it, of course now they don't provide any cds with a new PC but instead a recovery partition and the option to create restore CDs.
I created the restore cds so I could delete the recovery partition to free up room (also deleted the preinstalled games 50 of the damn things, and all other fluff) it is a sad state of affairs when you buy a pc with a 80 gig HD just to find you only have 50gigs free at first boot
.
Anyway does the Win XP Pro upgrade install on top of Win Xp Home? or is it basically a full install?
I don't see anything in the requirements stating you need to have any copy of Windows for a install.
I want XP Pro on this pc, just becasue I prefer Pro over Home edition. But will I be able to install on top of Home or is a format in the picture?
I just bought a Compaq Presario lappy and it has Win XP Home installed on it, of course now they don't provide any cds with a new PC but instead a recovery partition and the option to create restore CDs.
I created the restore cds so I could delete the recovery partition to free up room (also deleted the preinstalled games 50 of the damn things, and all other fluff) it is a sad state of affairs when you buy a pc with a 80 gig HD just to find you only have 50gigs free at first boot

Anyway does the Win XP Pro upgrade install on top of Win Xp Home? or is it basically a full install?
I don't see anything in the requirements stating you need to have any copy of Windows for a install.
I want XP Pro on this pc, just becasue I prefer Pro over Home edition. But will I be able to install on top of Home or is a format in the picture?