The IBM 970 has a completely different FSB to the one in use by the G3 and G4. It will require a new motherboard and chipset to make use of it effectively.
I imagine that it would be possible to make a CPU card that had on it the processor, a northbridge, fast DDR memory interface, and then logic to interconnect with an existing Artica S northbridge using the old G3/G4 processor bus. Of course then you would have an ultra modern CPU stuck on a motherboard with features 2 years old.
I imagine that IBM will be making a supporting chipset to go with the processor at the very least, hopefully supporting multiple 970 CPUs (I believe the 970 can scale to 16 CPU's in a system), supporting fast DDR / DDRII memory, and connecting to a modern and upto date southbridge featuring USB2, Firewire, NIC, SATA-150, etc.
I think that Thendic are using Pegasos as a brand name for their product range, not just to refer to the current motherboard.
