AMD has announced its dual core processors for the server and desktop market. Intel released their dual core chips earlier, with the Pentium D and Extreeme Editions which had impressive multitasking performance and would appeal to a few people. The Athlon 64 X2, as Exfoliate earlier mentioned won't be competing with the Athlon 64 FX range for pure single threaded performance. But it will be competing with Intel's Pentium D etc. It will be supported in the current S939 mobos, only requiring a BIOS update to get going. The Opteron x75s will also be backwards compatible, but only with S939 mobos supporting 90nm Opterons, again all thats needed is a BIOS update. The fastest dual core will be 2.2GHz and will be priced pretty heavily. The X2 will be launched officially launched in June, again priced heavily. This is probably due to AMD not wanting it to damage sales of its current K8 processors. I'll give a more detailed report later. (Trampolining at Nics). Anandtech article here.
