RAMBUS? Haven't seen that in a while, it's hella spendy and pretty rare. Looks like this model takes PC800 45ns (not sure if 40ns Rambus will work but I assume it won't). Prices are varying very widely for this ram and eBay is probly your best bet. Depending on how you want it (4x256mb or 2x512mb) you might drop anywhere from $70-200 on a gig of the stuff.
I'd still get it, though. Nice PC for only $100.