Hammers will do SSE2 and another enhanced 3dnow! set
The desktop chip is coming first
I couldn't say if the processor will be costly, it looks like since the processor and motherboards won't be normal, the cost structure won't either. As for right when it launches, probably costly...I don't know.
32 bit apps run much better, I'm told. They've said things about it, but those numbers change often enough I ignore them until release. (usually in the 20-25% range above Athlon XPs)