Partitioning in leopard

I keep hearing about a new feature in leopard called active partition or live partition or something like that. I heard its based off the work on bootcamp and allows you to add a partition to an existing drive without wiping what's already there. I have an external and really want to create a new partition without losing all of my data, but I cant figure out how to do this using disk utility in leopard. Does anyone have any info on how to do this?

Its under the partition tab in disk utility. Each partition has a drag corner to resize with.

but what if there was only one partition to begin with?

Click the + button under the partition list.

it's grayed out...

oh, forget it, i fixed it, it was set to master boot record instead of GUID