Need good mobo, case, and PS for dual Harpertown CPUs.

The Antec Sonta won't handle socket 771 Extended-ATX motherboards like the SuperMicro X7DWA $500.
(also remember FB-DIMMs for 771 server motherboards)

For a quiet E-ATX case look at the CoolerMaster Cosmos $150 after rebate.
Match that case with a Corsair HX-620 PSU $140 after rebate for a very quiet system.

Zipzoomfly has the same Corsair HX-620 for $125 after rebate.

Don't forget to analyze your actual computing requirements. It might be that two Kentsfield (single quad core) systems might be more effective (and less expernsive) than a single dual Harpertown setup.