OK, I think I got it down now.
AMD 8151:
Basically, this replaces the NorthBridge. However, since ClawHammer is going to integrate most of standard NB's functions (like the memory controller), it's not *really* a NorthBridge. Basically, the 8151 provides a HyperTransport AGP3.0 graphics tunnel.
AMD 8111:
Bascially, this replaces the SouthBridge. It also utilizes HyperTransport technology as an I/O hub, and is comprised of other features like integrating audio, storage, I/O expansion, security, and connectivity.
AMD 8131:
This device has two high-speed and independent PCI-X bus bridges. It seems like this will be aimed at server/workstation systems for SledgeHammer.
So ClawHammer will likely utilize just the AMD 8151 and 8111 bridges, with SledgeHammer adding the 8131 bridge to it's power.