Hi there
another endorsement for this -- use the stand alone BOOTABLE CD / USB version.
If for any reason you can't make this work then GPARTED also works fine --its been around longer so is quite stable although it's slower if you want to MOVE / RESIZE a large partition containing a lot of data.
Warning however be careful if you have Dynamic Disks -- this stuff tends to only work on "Classical" standard Partitions.
Cheers
jimbo