http://www.tyan.com/products/html/thunderk7x.html
ftp://ftp.tyan.com/datasheets/d_s2468_150.pdf
Just to make it clear... this one right?
(offtopic, damnit, where's a dual Barton mobo when you need one?/offtopic)
The inital problem is that , and i am assuming it, you dont have the motherboard yet, so there is no way of telling. Unless you can dig up some datasheets from Tyan or the AMD chipset.
http://www.amd.com/us-en/assets/cont...docs/24416.pdf
If i read it correctly ....er 6W ? If so, the passive cooler is more than enough ... even with a low airflow.
Anyway, IMO , you should first get your hardware and run a few tests on it before you get into watercooling it. If the datasheet is correct (just in case, test first).
If it's not the case, then you really should consider getting a block there. Iit's preferable to build/buy one, that to try a very ghetto approach on it.