However, I STRONGLY urge you to back up ALL your data before doing this. Playing with the partition map on the fly is not advisable. If something goes wrong the and partition map gets corrupted, you can kiss all your data good bye. Then you're spening $ for data recovery. So if you back everything up, the SAFE way to partition is to erase the disk and repartition it using Disk Utility off your Installer CD/DVD (or booted from another volume).