You may partition with Partition Magic.
You may partition with GParted or QTParted.
Here's another alternative, and I recommend it for two reasons: 1. It's cost-free (unlike Partition Magic) and 2. I've never known it to fail.
For some strange reason, sometimes GParted and QTParted leave certain options greyed out, even if the partition isn't mounted.
DiskDrake has always worked flawlessly for me. If you want to use it, here's what you do:
1. Go to the PCLinuxOS download page and download PCLinuxOS
2. Burn the ISO as a disk image
3. Reboot your computer from the CD
4. Sign in as guest (password guest)
5. Click on Install PCLinuxOS
6. Type in the root password (root)
7. Select Disk Partitioner (for advanced users)
8. DiskDrake will pop up. Use it. Then select Done.
9. Instead of installing PCLinuxOS, select cancel.
10. Reboot and install Ubuntu.