I haven't used Windows 7, but I thought it would let you re-partition your hard drive? I recall XP will.
At any rate, you'd like to wipe your system and start over. The best tool for the job is probably Mint's Disk Utility. If you boot up from the Mint live CD, you can find the Disk Utility under the System->Administration menu. I think it'll let you delete all of your partitions, at which point the Windows disc should let you create the new partitions it needs. I'm not familiar with Window 7's partition manager, but try to leave 20GB of space or so on the drive in case you want to come back and try Mint later.
If you want something more all-in-one, you can try GParted Live http://gparted.sourceforge.net
It's a Linux live CD which will let you do just about anything you want with a computer disk, including creating, removing and resizing partitions.
Of course before you delete all your partitions, you'll want to backup your files to another drive or CDs or something.