Go with the 65W EE version of the 3800 Windsor. Brisbane is 65nm, and it does run cooler, but its overclockability isn't significantly different from the Windsors. The worst thing about the Brisbane is that is has a higher cache latency, with the result that it performs slower than its Windsor counterpart (basically, 200 whatevers slower - like 4400 Brisbane=4200 Windsor).
Both the X2 3600 and the X2 3800 are good choices (I have an X2 3800 and love it)... but note there are two version of the X2 3600, one 2GHz w/ 2x256KB cache, and one 1.9GHz w/ 2x512KB cache. Since your son will be overclocking, if you decide to do with the X2 3600, its smarter to pick the higher cache version.
Good luck.