No-Cd XP Home reformat

Alright so I want to reformat my XP home computer (I've done all the file backups so I'm ready to go)but unfortunantly I do not have the cd (I bought this computer with XP already in it).

There's a product key sticker on my computer but I'm not sure how to reformat with it. Any help is greatly appreciated :D

(I might be able to get a hold of a friend's cd if that might help, but it's already used for his oomputer)

Just use your friend's CD. You can use the product key on your computer when prompted. Put the CD in, and follow the prompts....