What is your budget for this machine? I have been looking at high-end workstation / server configurations for my own use, and for around $1000 for the motherboard and process one can have the essentials for a 12 core machine:
http://www.newegg.com/Product/Product.aspx?Item=N82E16813182... (SUPERMICRO MBD-H8SGL-O Socket G34 motherboard for $244.99) http://www.newegg.com/Product/Product.aspx?Item=N82E16819105... (AMD Opteron 6168 Socket G34 115W 12-Core Server Processor for $769.00)
Total: $1013.99
That motherboard comes with onboard video and dual gigabit ethernet. The only other things required are a case, power supply, some RAM, and some sort of storage. All of this will be a lot less than $4000.