yah but i would also look at other auction sites not just eBay and did you ever consider buying a Linux machine ?
I know that can save you some money.
Also check out Dell's previously owned machines that come with a warrenty ?
http://www.dfsdirectsales.com/
http://www.dfsdirect.ca/
For example this is not a bad deal at $469.00
http://dfsdirect.ca/product.cfm?ProductID=13520