I experienced a problem with installing Mint alongside an existing working installation of XP the other day. As usual, the Mint installation from the live CD caused problems with the operation of XP and tweaking the H/D partitions was required to get everything working properly. The partition software on the live CD wasn't up to the task, nor unfortunately was a standalone version of gparted. Tried all sorts of 'work arounds' resulting in a real mess with only Mint working properly.
The solution/saviour was a program called parted magic, downloadable free from http://partedmagic.com/downloads/stable/
which performed all the necessary functions first time. This is a graphical program just like regular gparted but with no greyed out commands, it all worked perfectly - and quickly!
The offending Mint partition was resized and then moved down the drive making room to stretch the XP partition to a usable size in just a few minutes. Spent over a day trying other ideas and suggestions without success, hence my enthusiasm for this solution.
This program is now in my "Tool Kit" for next time......
Hope the above information helps others get out of trouble as easily as it did for me.