I have just learned a hard lesson about gparted, in the process of setting up a new netbook to multi-boot Windows Vista and Linux. Perhaps by passing it along, I can help others avoid stumbling over this.
I loaded Vista from scratch, telling it to create two partitions on the disk. It used 135 GB for the Vista partition, created a 100 GB Data partition, and according to gparted it left 1 MB of unused space at the beginning of the disk - although that space was not visible in the Vista partition manager. I believe that unused space has something to do with the Vista boot loader, but I'm not sure and I don't particularly care. That's a huge amount of space for Vista, which I am unlikely to ever use, so I wanted to reduce that partition, and use as much space as possible for the various Linux distributions I would be loading. The Vista partition manager would only reduce that partition to about 58 GB, and I wanted to squeeze more than that out of it, so I decided to boot the Ubuntu LiveCD, and use gparted from there.
The first time I resized the partition using gparted it not only reduced the size, it also moved the partition to the left, to take up that free space. Unfortunately, that rendered the Vista partition unbootable. It took a couple more tries before the light finally came on - the "round to cylinders" flag was set in gparted, so even though I wasn't telling it to move the partition, it was doing so on its own in order to shift it back to the start of the cylinder. All I had to do to get gparted to resize without moving the partition was clear that flag.
Two other things are worth mentioning. First, after you have resized a Windows partition using gparted, the next time you boot Windows it will automatically check and clean the partition. There's nothing wrong, it will only take a minute or so to run, just let it go. Second, once you have started a Move/Resize in gparted, if you interrupt it you are almost certain to end up with a corrupted (proably irreparable) partition. Except in case of extreme emergency, don't ever abort a Move/Resize operation!