The resize function is used to resize a partition and, if applicable, the filesystem that resides on it.  To resize a partition you must first select it in either the partition diagram or the partition list (when the selected item is empty space, this function is disabled).  Only some filesystem types (NTFS for example) can be resized.  A dialog box will prompt you for the new desired size (which can be in cylinders, sectors, or megabytes).  Before resizing a partition, you must commit any outstanding changes using the write changes function, or else undo your changes using the undo function.  A resize operation can take a considerable time to complete, and is very invasive.  Backing up all important data is strongly encouraged before proceeding.  Resize operations can and do go wrong from time to time (though it is not common), potentially resulting in the loss of the entire filesystem.  Once a resize commences the data is physically rearranged on disk, so you cannot subsequently use the undo function.

If Partition Logic cannot resize the filesystem on a partition, it will still allow you to proceed to resizing the partition, but doing so is strongly discouraged if there is any data on the partition that you want to keep.  Enlarging a partition but not the filesystem will not increase the free space in the filesystem.  Shrinking a partition but not the filesystem will result in any data beyond the new size being lost. "

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Taken from their manual.

Bottom line....if the data is important to you...don't do it with this proggy.

I have had no problems doing it with Partition Magic, a proprietary software, though...