This Toshiba 17 inch laptop with a 250 GB drive, and Vista Home Premium, and 3 Gigabytes of memory is on sale at Computergeeks.com for under $400. It has a Celeron processor and, for another $119, you can upgrade it to Windows 7. Under $500 and a lot of computer for the money, even if it is refurbished.
Hat tip to Futurelawyer. (Ignore the anti-Apple snark)