Go for a Opteron 165 or a Athlon X2 3800+, best bang for your buck.
THe opteron would probably better since people get mad OC's with those with a better HSF.
Both are socket 939.
If you got a pentium I would have to KILL YOU. The 820 is a sucky chip! Go for an X2 or the dual core opteron (like 165 like I said above). THey should be cheap enough and you could get great OC witha decent Mobo. The X2 beat the Pentium in like every benchmark.
-dragonx