There is no "uninstall" really. Pop in the Windows CD and boot in to the setup (blue screen), press F9 to agree to EULA (unless, well, you don't agree), select any/all partitions and hit "D" , "enter", "L". Then select the unpartitioned space, hit enter twice and it will setup a new partition. Select full NTFS format (not quick) when prompted.
I think that's it. Might have forgotten a step or two, but that's the idea.