850, RDRAM? expensive combo man!!! it won't support 4GB. 2GB is the max. plus getting 2GB ram (in whatever stick config) wud be hard and expensive for you. it'd be better to sell this mobo and buy another socket478 mobo (searching a bit can get u one) and going in for 2GB or 4GB DDR2 ram. that will actually work out to be cheaper than thinking of buying 4GB RDRAM.
btw, 4GB RDRAM is only supported in intel 820 and intel 860 chipsets.