AMD zone alos has an FAQ at http://www.amdzone.com/articleview.cfm?ArticleID=1195. Sample...
Q: Will Apple use Hammer CPUs in their computers?
A: We have heard that AMD personal are at Apple working to get them on board with Hammer. OS X's Unix underpinnings would allow for a relatively painless transition. Apple is a member of the HyperTranport consortium, and seems to have taken a liking to Nvidia's nForce chipset so anything is possible. The inability of the G4 to scale to higher MHz may push Apple to another CPU supplier, but Steve Jobs ego has relegated Apple's market share to small percentage for so long they may not be able to accept any sort of rational change.