The manual spec' states that the RAM supplied is "32MB SSDRAM on-board, expandable to 160MB with one 3.3V 144pin DIM SDRAM module." In actual fact it came with 64Mb. I do not know what the motherboard bus speed is.
My guess would be that you got the basic model already equipped with an additional 32MB-Module. So start looking for that and then you know what your replacement should look like
