well,
I installed my dualcore after I redid the wiring to make everything go behind the motherboard plate, looks very clean now.

Anyways, the cpu was recognized, I rebooted, made a new entry in the registry, and installed a patch and all is well now.
With my opteron 146 @ 2.5Ghz and X1950XT @ 675/2000 I scored around 3000 in 3dmark06, which was kind of ok, but not really.
Now I installed the x2 3800, clocked it up to 2.5Ghz, kept the videocard at default and my score went up to 5686, which is pretty nice I think.
All games run as smooth as they did when I had the opteron in here, so no performancedrop whatsoever.
Seems the patching has done it's job right.