In Windows 7 you don't need any third party software to resize partitions anymore. You can do it right from the settings screen. This is included since windows vista.
To get to this utility, open up Control Panel, and type in "partition" into the search box you’ll immediately see the link show up:
In the Disk Management screen, just right-click on the partition that you want to shrink, and select “Shrink Volume” from the menu.
In the dialog you enter the amount you want to shrink, so NOT the new size, but how much you want to "slice off"
When this is all done, you have some new space left ! you can add this to an existing partition, or create a new one.