It used to be that multiple cpu computers meant that you had to have two (or even four) cpus on the motherboard. Now both Intel and AMD have DUAL CORE cpu's, the AMD solution is to put two Athlon64 cpus on a single chip, this is possible because AMD has their memory controller on the chip. Intel's memory controller is off the chip and this makes their dual cores less efficient than the AMD, some article call the Intel solution two "virtual" core cpus. Here's link explaining two cpu's on one chip for the AMD.
Now that dual core chips are out, you can even have multiple dual core chips on the same board, and in the future AMD is going to put FOUR cores on one chip (then 8, then 16, etc.) The real advantage to having a multicore cpu or dual cpu's on the motherboard is in multitasking. This really helps out for those who have virus programs scanning in the background, burning or ripping cd/dvd's while doing other chores on the net, in word processing or using a spread sheet. My new computer doesn't "lag" on me, like my old single core P4 did when task loaded. Most programs and games are currently single threaded and don't derive any great benefit from dual cores or dual cpus, this is changing though, and in video there are a number of programs that can make use of both cores, CCE Basic is one of these.
The 3800+ X2 chip that I have is now only $315.00, a real steal. And I have it running at 2.5GHz on stock v-core, so I have a AMD 4750+ X2 ;) I'm getting DVDRebuilder/CCE Basic encodes in around 40 minutes on large movies. DVDShrink on the same large movies with deep analysis and max quality is less than 10 minutes (not including burn time). A small fraction of my 2.0GHz P4 system.
So I love dual cores, and won't ever have another computer that isn't multiple core. Most/all socket 939 mobos support the X2 chips, some require a bios update before they will recognize the chip. Look at newegg.com the list a comprehensive lineup of motherboards that support the Athlon64 X2 chips.
