I put together a Linux computer this week based on an Atom D510 (dual core, hyperthreaded). It came to $250 with a 500gb HD, 2gb RAM, case and DVD drive, though I could have saved $30 by omitting the opitical drive and installing from a memory stick. It has the added benefit of being passively cooled -- it is almost silent, the only noise being what is emitted by the harddrive. It's even quieter than my Macbook Pro.