gparted is a great partitioning tool - I have used it to resize FAT, NTFS, EXT[2..4] and haven't run into any issues as of yet. However - with all disk operations there is always the possibility of failure and that should always be weighed during resizing.
Make sure you have nothing mounted to the drives you're attempting to resize, ensure that you have ample CPU and RAM to perform the operations. If you're on a Laptop make sure it's plugged in and that it won't suspend or hibernate while performing these operations. Lastly this can be time intensive - my last tip is, while gparted is running it may appear unresponsive or frozen. Just let it finish.
Indeed - my first introduction to Linux systems was using a GParted 'image' to boot from and resize the my VMware Fusion virtual PC's hard drive. I've since used it maybe a dozen times for doing this, on different VMs, for XP and Win2k3 (both NTFS). No problems at all.
If you haven't done it before, just take your time and carefully read all the pop-up dialogs and messages before pressing 'Yes'. :-)