I have 384 in my Rev. B, and it can go up to 512. You need a low profile 256MB SODIMM for the bottom slot, but the top slot can hold a high profile SODIMM.
If you're lucky, you can find a 512MB stick that will go into the top slot (for a total of 768MB with another 256MB stick.) I still haven't found a place to buy RAM that wont show up as a 256 stick because of the chip density.
I have to say, low profile rams are expensive compare to the regular profile. Having said that, I used to own a rev B 233 iMac that I expanded the ram (now in the hands of a friend) and currently own a CUBE 450 and a G3 Pismo 500. The Pismo, according to Apple and other credible third party ram vendors says that top slot can take a regular 512 ram but the bottom needs to be a low profile. Guess what...that's a lie. I currently have a regular profile 512 in the bottom and a regular profile 256 on top. I experimented with it individually and caused absolutely NO problems for the last three years.
I am using the same in my Pismo. I have had it running this way for 2 years. If it is causing problems...then it is very slow in revealing any ill effects.
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I have 384 in my Rev. B, and it can go up to 512. You need a low profile 256MB SODIMM for the bottom slot, but the top slot can hold a high profile SODIMM.
If you're lucky, you can find a 512MB stick that will go into the top slot (for a total of 768MB with another 256MB stick.) I still haven't found a place to buy RAM that wont show up as a 256 stick because of the chip density.