You won't have any unallocated space until you shrink the current partition.
You can use Windows 7's disk management utility if you wish. Partition or Volume - Shrink
If you want more control you may want to consider using Partition Wizard, as this tutorial explains. Partition Wizard : Use the Bootable CD
Basically, you create a Partition Wizard boot disc that you boot into, carry out your partition changes, apply them, and then boot back into Windows when you're done.