Well the best way to do so would be to back up your data, then reformat and re-install Fedora. Also, Fedora 13 is out
If you don't want to go this route, then from within Fedora you can delete the Windows partition, format it as EXT3/4, and then have a separate data partition. I believe if you boot from a LiveCD you can extend your primary partition as well (as it wouldn't be mounted for the LiveCD, but I'm not 100% sure on this), but you cannot do so from within your Fedora installation. You'd have to edit your Grub/Lilo config file as well.
There's a few different routes you can go, but I'd say a full re-install would be your best bet. If you don't want to do this, you could try the other method I mentioned.