Marvellous Feature!
Shamelessly borrowed from
http://www.hardmac.com/ and the boring bits edited out.
Very useful and intersting Mac Techy Site, is actually a French site, the French Portal can be found here
http://www.macbidouille.com/
Leopard incorporates partition resizing tools in the native disk utility app, and we will show hereafter how to proceed.
First, select the partition to be decreased in size, then using the bottom right corner or the "size field", enter the new storage space value; then apply those modifications:
To add a new partition, click on the "+" button:

We called it "Ma Partition".
Then click Apply, and ... that's it! Done. However, one would not be able to mode a free space from one partition to another existing one; so partition management application can still be useful. This new feature seems to work for all Leopard-supported Macs (Intel, G4 and G5).