Well...it depends on how the partitions are setup. Is the XP partition behind the mac partition? If so you should do something like this:
1. Download MyDefrag: http://www.mydefrag.com/Manual-DownloadAndInstall.html
2. Run it on the XP machine...this will move all of the data to the front of the drive.
3. Download the Gparted LiveCD and burn it to a cd: http://gparted.sourceforge.net/livecd.php
4. Run the LiveCD...if you need help with Gparted I can walk you through it...but since you're running Linux I assume you have a working knowledge of partitioning. The basic idea is to add more space at the end of the XP partition.
Let me know if you need any help!
EDIT: Wait a minute...just realized his is running in a virtual environment as well. In that case...what virtual machine is he using?
Edited by A Future Pilot, 26 November 2011 - 06:33 PM.