Below are a few available Open Source Partition Editor packages. There are more, and if you are interested you can do a search for "open source partition managers" from your favorite search engine and find one you might be interested in.
Of course, since you are reading this you are either interested in or intending to install Ubuntu Linux on your computer, either in a dual-boot or multi-boot configuration with Windows (or other Operating System) or as a stand-alone Operating System. Although in some circumstances the "Alternative Install" disk is required, the vast majority of you will be using a LiveCD version, with which you can not only install Ubuntu, but can run it directly from the CD to try it out as a demo first.
When you boot to the Ubuntu Live CD and select "Try Ubuntu without changes" from the beginning menu, you can run Ubuntu from the CD. You also have access to various tools which includes the Partition Editor. From the Launch Bar at the top of the desktop, select "System/Administration/Partition Editor." This will run the partition editor included on the disk, which the installer also uses to prepare your hard disk for the actual installation. It is the Partition Editor which I used to create the screenshots for my demonstrations.
GPartEd Live CD
SourceForge has compiled a partition editing tool called GParted Live CD. This is a special Live CD whose focus is wholly on partitioning hard drives and manipulating those partitions. It's a very fine tool and one which I use quite often in my disk operations.
Parted Magic RAM-boot Version
Parted Magic also comes with GParted, but a standalone, installable version that boots and runs off RAM is also available in deb, exe, rpm, and sh formats so that no CD is required to use or run it. HowtoForge has screenshots and instructions on using the Parted Magic RAM-boot approach.
Special Section On Back-up Tools
While the Community Wiki has a section on Backing Up Your System, it concentrates mainly on backing up an already installed system and the data files on it. When you are preparing to install Ubuntu and need to back up your existing partitions and disks in preparation for partitioning operations, you will need a back-up tool independent of an installation.
Clonezilla Live CD
Far and away my favorite Live CD backup tool is Clonezilla. It will allow you to back up and restore not only separate partitions, but create images of your whole hard drive, as well.
The partition imager which Clonezilla is based on, but not as automated as Clonezilla. PartImage Home Page
SystemRescue Live CD
The SystemRescueCD is another powerful suite of backup and recovery tools.
Another backup tool I have found is PING. I have not tried it, but it apparently will not only back up partitions and hard disks, but the Master Boot Record and BIOS settings as well.
There are undoubtably others, but those I have mentioned are fairly well known and runnable from a Live CD. Others can be found through your favorite search engine, should you desire to find one that will fit your particular requirements.