I've used the
System Rescue cd to do this - there's an app on there called "qtparted" that should allow you to do what you're asking. I'm pretty sure there's a few other apps around that will do it as well, but that one's been sufficient for my needs, so I haven't tried anything else (and it's quite similar to Partition Magic, which I used for years before I made the switch to Linux) It goes without saying, but I'll say it anyway: BACK UP ALL IMPORTANT DATA BEFORE USING THESE TOOLS! I've never lost any data using those kinds of tools, but there's always a first time.
Good Luck!