I see on LifeHacker
Next I started up the install and found that Vista will only install itself on a primary partition. If you choose the C: drive where XP is already installed? Vista asks if it can rename your Windows folder "Windows.old." Uh, no thank you Vista. To get dual-booting to work, you have to create another primary partition where Vista can live alongside XP in peace and happiness.
Free partitioning utilities (like the one on the XP setup disk) delete all the data on the disk when they create new partitions. That's not very convenient. Norton's commercial product called PartitionMagic, which you can purchase at Amazon for $43 (after rebate), however, can create a new partition out of free space on your C: drive without killing the rest of the files. That's what you want. UPDATE: Astute reader Barron says that the GParted Live CD also works and it's free. Thanks Barron!
Download of the Day: GParted live CD
In the past we recommended repartitioning your hard drive with a Linux live CD, but if all you want is partitioning, the GParted live CD is the way to go. If you've never burned an ISO before, check out the free ISO Recorder tool mentioned earlier today.
Looks good: A quick look at the GParted live CD