Creating a partition on main o/s drive in leopard

Hi friendly folk

I have just purchased and set up a new Mac Pro running leopard 10.5.1.

I only have the default 300gb harddrive with it as I intend to buy an additional one soon, however until I get that new on it would be very handy to partition the one I have.

Now, I've never known a great deal about this side of Macs despite having used one intermittently for a long while, but in old O/S's I did not think you could create a partition on a main drive that the O/S was active on.

However in leopard, it seems to give me the option.

My question is, has leopard made it possible to create a partition on the main and only hdd? I know this is possible on a PC in Windows!

I did try to just do it in disk utility, but it seemed to just stick on 'partitioning' for ages (read >10minutes). Now it didn't crash the machine or anything, tho it did freeze the window whilst it was 'working' and I don't want to do it again

Any advice would be greatly appreciated even if it's 'buy another hdd, that doesnt work'

Thanks
Manualsaurius