TigerDirect offers the refurbished Dell Optiplex 775 Core 2 Duo 2.33GHz Desktop PC
(no monitor), model no. RB-755E6550SFF, for $229.99
for shipping. That's only $50 more than a similar refurbished Optiplex 755 with half the RAM and half the hard drive capacity sold elsewhere. Features include an Intel Core 2 Duo E6550 2.33GHz dual-core processor, 4GB RAM, 160GB hard drive, DVD-ROM drive, Gigabit Ethernet, keyboard, mouse, and Windows 7 Professional 32-bit.
A 90-day warranty applies, although it's unclear who supports it.