If I recall correctly, Windows does not recognize a drive that is already partitioned and formatted with something like ext2 or 3 (the typical Linux file system.) This only one of MANY ways in which Windows is an inferior OS to Linux, but that is maybe not what you wanted to hear....
I think all you have to do is delete all the partitions. You can do this with any number of utilities, including ones found on "Live CD" versions of Linux. If your Linux is a live CD, just boot up from the CD, open a terminal, and use fdisk or cfdisk to delete all partitions. In the menus, you might also find GParted.
If it still won't recognize the disk, then you can wipe out the whole front end of the drive using:
dd if=/dev/zero of=/dev/sda bs=512 count=63
instead of sda, you might need to use hda. fdisk will verify which is correct.
More generally, there are a bazillion utility CDs out there that will do this.