You have drives so why not go to newegg or tigerdirect and buy a barebones. Tigerdirect is selling dual-core 3.2Ghz machines for sub 300.
[link|http://www.tigerdirect.com/applications/SearchTools/item-details.asp?EdpNo=2984884&Sku=I69-2146%20D|http://www.tigerdire...&Sku=I69-2146%20D]