Sandy and Ivy both contain execution cores, graphics, memory and pci-e controllers.
The chipset is just a south bridge with USB, SATA etc peripheral and I don't see why it should not be compatible if it's connected to CPU via same DMI bus.
You would need new CPU, mainboard and memory. Rest of what you already have will work just fine with new setup.
AMD will be releasing brand new architecture called Bulldozer somewhere summer time with desktop options with up to 8 cores. You can read about them a bit on Hexus:
http://www.hexus.net/content/item.php?item=27411
http://www.hexus.net/content/item.php?item=26082
Sounds promising but I'd wait for new chipsets for this new arch as well although it is compatible with latest AM3 boards. Perhaps next year's 28nm shrink of Bulldozer will be drop-in compatible with 890/990 chipset boards but at this point it's just an assumption. Though with future-proofing of sockets AMD is known to be more friendly than Intel.