Nik I got confused with your post.
1) Why do you want the Opteron 146. Actually, I dont understand why AMD make Opteron 1xx. The only advanatage Opteron 1xx can have over the AMD consumer line is ECC memory (greater stability).
2) The opteron will not fit in that ASUS board (socket 939) since Opteron use socket 940.
3) I dont like on-board video for workstation. It's only good for server or low cost computer.
4) Just the up front cost, I dont think you can ever build a system cheaper than Dell (after promotion). Now thinking about total cost of ownership, most computer components have one year warranty. If later something fails, it would be much easier to deal with one reputation manufacturer like Dell.
5) The labor cost of assemblying a computer is cheap. Most of the time it is between 20-50 bucks
When you build a system, you should at least have a clear answer to these questions:
1) What is the purpose of the system?
2) How big is your budget?
3) How important is time to you?
Good luck building your system. By the way
www.2cpu.com was the place I used to hang out.