Sorry rereading my post and it did seem a bit fluffy.
Anyway, you have to reformat the partition. You can do this from the live CD or with a utility of your choice. Gparted is on the Mint CD, so you can try that for convenience sake.
Now getting rid of the partition is one thing.
Next, you should try to boot your computer, two things might happen:
1: Normal boot, you arrive on Windows = great. You should not need to do anything else.
2: Or Boot goes wrong, and the windows partition will not load up (This is often because GRUB, the Linux boot loader, overides the windows' one, and when you reformat, the computer does not know what to boot up)
The solution to this is to simply go into windows recovery mode:
Here is a link to a tutorial which goes through the motions of repairing the boot:http://www.vistax64.com/tutorials/163304-dual-boot-using-free-partitioning-software.html
Whatever you do, do not despair or overwrite your Vista installation. Everything should be ok, and people on this forum will always be glad to help.