I purchase all of my hardware from
www.newegg.com
I have probably spent $5k in parts over the years. They are not the cheapest, but they have good service. Their credit card authorization proces is a cumbersome, but I don't mind.
PC3200 ram is standard 400mhz memory. Memory prices are dictated by speed and quality. 400mhz is the clock speed, but better memory has lower latency. If you are going to bother upgrading, put in a GB. Some memory has ECC(error correction code). I am not familiar enough with MACs to know.....but I doubt it. Thats typically reserved for servers.
EDIT: Do you have a Frys Electronics around? (isn't there one in Berkley?). Go see if they have any cheap sticks of PC3200 'no name' memory on sale. Take it home and slap it in. If it works, great, if not return it. Iam all for abusing Frys liberal return policies....