Hi Astrojax,
I assume your Linux is installed in a patition of its own.
Simply remove or format this partition, that's it!
If you have grub or lilo installed in you Master Boot Record (the "wanna boot Linux or Windows" thing at system start
, you can remove this by the MS-DOS Command
fdisk / mbr
wich is still available in the Dos successor known as Windows XP.
HTH, Peter