Lots of glitter, but what does it mean?

I realize AMD is competeing with clockspeed numbers thus the XP 1800 and so on. My question are there differences between the XP’s and the MP’s. If I understand correctly the XP CPU is built for multi thread processing… And I can imagine that is true also for the MP’s. Are there any other differences?

End result: I’m building a workstation with an ASUS A7M266-D. What cpu deserves the socket A slot?