CPU Sockets:

Socket AM2:
Hypertransport 2.0 (1Ghz)
Socket is 940 pins and will fit in AM2, and AM2+ Sockets
Supports Dual Channel DDR2 Memory

Socket AM2+:
Hypertransport 3.0 (2.6Ghz Max)
Socket is 940 pins, Will work with both AM2+ and AM2 Sockets.
Socket AM2+ cpu's will work in AM2 motherboards depending upon bios revision and chipset.
Supports Dual Channel DDR2 Memory

Socket AM3:
Hypertransport 3.0 (2.6Ghz Max)
Future AM3 Motherboards will support up to 3.2Ghz with Hypertransport 3.1
Socket is 941 pins, Will only fit AM3 Cpu's in an AM3 motherboard.
AM3 Cpu's are backward compatible with AM2 and AM2+ motherboards, depending on chipset and bios revisions.
Supports Dual Channel DDR2 when run on AM2/AM2+ Motherboards.
Supports Dual Channel DDR3 when run on AM3 Motherboards.