How to Replace System Drive?

Ok, I did a search and didn't find a procedure to do this, but this is what I am wanting to do:

I want to replace the 36GB SATA system drive (WD Raptor) in my G5 Powermac with the 72GB model. Is there a way to create a disk image of the system drive, replace it with the new one, and then apply the image to the new drive and be up and running? I do not want to have to reinstall everything, and I have ample space on my secondary drive for a 36GB image (actually, system drive is at 17GB utilization.) I thought you could make a disk image with the OS install CDs... am I wrong?