Chistropher Breen of MacWorld has outlined a method of partitioning using Disk Utility so that you don’t loose any data from partitioning an active drive. In this article “Delete Mac partitions without losing data” not only does he describe how this is done but he has a video that clearly shows how to accomplish this. This is more than useful as I can’t think of how many times I have repartitioned and lost valuable data.
There are two excellent high end tools to also accomplish this. iPartition is a tool that is strictly dedicated to repartitioning. Drive Genius is an all purpose drive tool for maintenance and repair that also repartitions a drive. Be careful when you repartition a drive as it is too easy to forge that you have valuable data in a partition.