Hey Datalogger, running 2x client on P4's with HT was alleged to increase output by 20%, compared to just running 1 client. Athough Stanford always prefer a quicker turnover of units, and prefer you to run 1 client on HT boxes; and with P4's just go for high Mhz & big cache, check the specs of chips on the Intel sSpec Finder RAM size is not too crucial on the vanilla client, most of my rigs have had 512mb but I wouldn't expect any problems running with 256mb to be honest.

Personally I'd look at a budget AMD x2 or even C2D system, in place of a few P4's, however if you are hell bent on getting older kit off ebay, I'd go for Semprons or A64's, for that gen of chips AMD have better power/performance imo. Having run a few benchmarks in the past, my Sempron 1.8Ghz/256k(iirc) is a better cruncher than my P4 2.66/512k. Hope that helps man