Sorry - I missed the bit about memory - that'll teach ya for posting a doublet
Again not a simple answer, the limitations are imposed by the hardware bit addressing and the firmware coding. Quite often you can put more than the specified maximum RAM and get away with it, my Pismo has 768M whereas the specified max is 512. How far can you go? I'm afraid it's a case of suck-and-see and there are three main issues:
1) What can you put in without the Mac crashing / freezing
2) How much can be put in and recognised
3) How much can be put in, recognised and used.
It is important to appreciate the difference between points 2 & 3, the OS when booting may recognise XX amount of RAM but running programs may only be able to access X amount of RAM.
I can only suggest you Google and find how far others have pushed your specific model