Does it matter if I put DDR or DDR2 RAM in my laptop?

I don't even think you can seat the ram in correctly.

Look at the Notches (the little hole at the connector area

SDRam

DDR2 Ram

As you can see, SDRam has two notches while DDR2 Ram has one slightly to the left. Not to also mention that laptop DDR2 Ram is smaller and more squarish.

• Click on over to > ***http://www.crucial.com/***
  
• They should know what type of memory you can use in your PowerBook G4
  

No you can't use DDR2 instead of DDR. As for how much ram you can install either you can open it up and look or you can install a program that will tell you exactly what is in your computer and what the maximum supported upgrade would be. I can't remember the name of the program I used in the past but I think it started with Si

Edit: I found it. It's "SiSoftware Sandra" which you can download if you click on the like I provided.

PS: I'm not sure if you can use it on a mac or if there even is a mac version of the programm

Some motherboard only take one type of RAM and if you mix what you use it might break the RAM and/or the motherboard. And again it might not even fit.