To expand a little:
1. Defragment your Windows installation.
2. Run your live Mint CD and start gparted.
3. Select the Windows partition and shrink it.
4. Move your Linux partition(s) "sideways" to take up the space freed up after the Windows one.
5. Expand the Linux partition (/home if you have it) to use the free space that's appeared after it.
Make sure your data is backed-up before you start. Gparted is safe, but there is one very minor risk: if you are running a desktop with only mains power and there's a power cut while gparted is moving or resizing a partition, that partition will be wrecked. But how how often does the power fail?