have you bought the s2882 yet? if not, use Tyan Transport GX28 barebone featuring S2881G2NR (dual-core ready!).
if you must use s2882, then buy the new 'D' version s2882g3nr-D which is dual-core ready! the old version (without 'D') doesn't have the VRM required for dual-core chips, therefore you can't upgrade CPUs to dual-core.
if you already have the s2882, then chenbro RM117 is your best fit. remember to order the 1U Air duct for Tyan S2882 (chenbro part #83-503117-002 ) and dynatron A51 (180-degree) all copper 1U opteron heatsink. this setup will end up to be more expensive than tyan GX28, though!
I have already puchased the s2882. I purchased it last year. So I assume I have the old version
The heat sinks seem to cost only 20 bucks a piece from directron. Air duct seems will run about 40 bucks. I didnt realize it did not come with a backplane. So I guess thats how it works out to be around the same price. But the other I would need to get the two heat sinks plus some type of duct, I assume.