Switch out sockets, either for conroe when it comes out, or if you want to do it sooner you can't go wrong with the AMD X2's. I wouldn't recommend going with Intel until conroe.
As fun as the 478's are to overclock, the platform is dead. Only one or two 478 motherboards support PCI-E, they're really hard to find, and not very good overclockers. That's not only important for gaming, but also AFAIK there won't be any new AGP cards that support DX10 coming out, and Vista is going to make major use of DX10.
-z