Is 1.5 gb ram enough for Lightroom

I have a Power Mac G4 dual 867 cpu's with 1.5 gb ram
Often in light-room when using the brush, the mac stalls out and get very sluggish. If I installed more ram would it fix that?
When i open the machine up it has cards in every slot (4)
Dose the Mac use the same ddr ram as a PC?
What would be my bet choice for new ram?

Thank You,
Ken.

Im not sure whether it would be the processor or ram that would make the difference.
Im assuming that since you arent on an intel that its going to be quite a bit slower. 1.5GB of ram should be enough for viewing images in lightroom.