I suggest go with AMD because an AMD system will be the cheapest to handle multiple virtual machines at once.
MSI 770-C45
ECS IC780M-A2
MSI 870A-G54
There are a lot more than this list. You may want to add NIC because Realtek NIC are OK for desktop, but not for servers. You will need to add a video card, so you can have access it during setting it up. I suggest a nVidia graphics card. You could with AMD/ATI graphic cards but only use drivers from Xorg for AMD/ATI cards for reliability.
Using desktop components for a server is OK, but I suggest find computer cases that have multiple 5.25 inch drive bays. About 9 bay should be at least for a computer case to house a server. You can then use removable hard drive bays that will hold three to five hard drives. You can setup RAID-10 or RAID-5 for better performance for VMware.
Like I said eariler, use ECC memory for better reliability and stability. Desktops do support ECC memory, but almost all AMD systems do since K8 or Athlon64 processors. Intel include it but only for the enthusiasts models. For both Intel and AMD systems the memory controller speed for DDR2 is 800 and for DDR3 is 1066. Any higher is over clocking the memory controller. For even better reliability and stability, you should see voltage of DDR2 to 1.9 volts instead of 1.8 volts. For DDR3, you should set the voltage to 1.6 volts instead of 1.5. ECC memory may also be stated as server memory, so you may have to go in that section for some eRetailers like newegg.com. For any desktop system filling up to all banks should have two double-sided and two single-sided memory or four single-sided memory. Double-sided memory puts a noisy load on the memory controller, so any more than two double-sided modules will hurt stability. Desktop systems usually take unbuffered memory.
If you want a six core processor, the following link shows the motherboard compatibility for a six core AMD processor.
http://www.anandtech.com/show/3678/p...rted-at-launch
I still recommend do not run heavy applications on a virtual machine because performance will suffer. Your server apps will not load a virtual machine as much as multimedia programs. Accessing a virtual machine that is running a multimedia program like Mythtv over 1 gigabit network will have poor performance. You will need a 10 gigabit network to handle it, but still multimedia programs will suffer performance. For example running The Sims 2 under VMware Workstation 7 or higher, will have poor performance rendering about 5 to 10 frames a second. You will get better speed if you use multimedia programs when they are running on the host and not in a guest operating system. Mythtv includes VA-API/VDPAU to aid in decoding multiple video codecs. I have tested VMware with multimedia and it is not pretty. Video and sound playback relies on the CPU in VMware compared to them being decoded on the host. Basically running multimedia programs in VMware will penalize these programs by about five times compared if they ware run on the host.
If you still do not believe me, I have used VMware Server (GSX version) to play Starcraft I. It plays it fine, but everything slows down when there is a lot of activity or the game play is busy. Even the inputs are slow. I upderstand the penalty when run Starcraft in VMware, I can deal with it because VMware is the only way the game plays or draws correctly compared to Cedega or WINE. I was using the same computer that the virtual machine is running.
If you use VServe for multimedia appications or Mythtv then go for it because the penalty is only about a little or programs will seem they are running at host speed. The VA-API/VDPAU could be used, but I am not sure.
