This case totally rocks in terms of strength and cooling:
COOLER MASTER Praetorian 730 RC-730-SSN1 Silver Aluminum ATX Mid Tower Computer Case - Retail
to go along with this good power supply:
Antec TRUEPOWERII TPII-550 ATX12V 550W Power Supply 115/230 V UL, TUV, CB, FCC CLASS B, CUL - Retail
Dual core Athlon 64's (X2) work like multiple processors. It has two cores on one die making multitasking more efficient without slowdowns we're likely to see on single core CPUs.