Adding a Mac partition to a FAT32 external drive without loosing data?

Hello everyone!

First of all, I'm new here! Yay, right?
Been reading the news on the site for some time, but not so much the forums.
Actually I'm also pretty new to Mac, bought my first this August! So far, I'm extremely pleased with Mac and can't understand
what I've been doing on PCs for so long. It's a MacBook Pro 2,2Ghz that I bought, by the way.
So, hi!

Second of all, I'm hoping I'm posting this to the right forum? I saw there are MacBook Pro-special forums etc, but this is more of a general question that applies to all Macs, right? Anyways, hope it's in the right one. Otherwise please advise and I will "move" it.

To my problem!

I have bought a 500GB external drive which I loaded all my previous things from my PC on, before selling it. So I have a complete copy of everything there, fills up 278GB of that.
It's formatted in FAT32, I needed to be able to write to it in Windows, and then in the Mac. Besides, I use Bootcamp so it's nice to be able to access it in both ways.

But now I want to add a Mac OS Extended journaled partition to this one, because I need to be able to have files larges than 4GB on it.
It should be at around 150GB.

So, I know I can do this with Disk Utility, create two partitions.
But how do I do this without loosing the data on the already existing FAT32 one?
Disk Utility says it will replace it!

Thanks for any advice and help!

Regards,
Jonathan

 

I do have Leopard!

I'm probably an idiot, because I can't find how to do this in the Disk Utility. I can only create new ones.
It keeps saying "A new volume will be created" and all the fields are greyed out when I have "Current" selected.
Sure it can do this with FAT32?