Check this thread.
Check my experiences in [link|http://z.iwethey.org/forums/render/content/show?contentid=185006|this] thread and Greg's replies.
Bottom line - use the right tool to work on the partition and you should be fine. Backup anything you can't afford to lose (but you do that anyway, right?). You shouldn't need Partition Magic, but will need a similar gnu tool.
Cheers,
Scott.