Hey,
Now Im not to sure about this but I believe the K8 is the SledgeHammer series. The K8 was originally supposed to be a 64 bit processor. The Hammer series is going to be AMDs first 64 bit series. I don't know if it will be named the K8, but I'm pretty sure it wont run on most current platforms. The Hammer series should have backwards compatibility for 32 bit apps though.
Just my 2 cents,
Timothy Stankus
One of the First AMD Athlon Users =)