...the best thing to do is takeout the ram in your laptop go to best buy and show it to them...
your maximum ram is 3gb to 3.5gb. don't go more thats if you have 2 slots underneath.
I don't suggest the first part. Knowledge is better than Ignorance, in this case - learn a little about what you're buying and save some cash.
As for the second, I don't recall him saying he had a 32bit OS, or any specific chipset that would limit it. But 2GB should fit most people's bill anyway.