Use at your OWN risk (or that of your data's risk): AKA Where the Jebus are my files?
There is no decent way to do it for free.
You could attempt to use pdisk to do it, but unless you're conversant in UNIX and love reading man pages, it might be a touch nut to crack.
There are a few products out there (for $$$) that will resize your partitions or partition an unpartitioned disk. But there are many articles on many forums and Mac support sites that detail problems with both. IMO, there are no 3rd party repartitioning apps that can do the job SAFELY.
But if you must:
iPartition
VolumeWorks
PartitionToolkit
Again, if you want to do this that badly, make sure you have an excellent back up first. And if you do get an excellent back up, why not just use Disk Utility to erase and repartition your disk and then clone everything back from your back up? It's safer & proven effective.