Build or Buy?

I will be obtaining a PC during the summer for testing purposes and would like to know: for $250 is it better to build or buy a computer. There are some dirt cheap refurbished Dell PCs on Ebay, but I worry about their quality. 

I already posted about this, but I want to run Linux on the computer. One of my friends told me he thought that pre-made computers were for some reason easier to install Linux on, although he could have been mistaken. 

Build Idea: http://pcpartpicker.com/p/3NfU6

Pre-Built Idea: http://www.ebay.com/itm/Fast-Dell-Optiplex-Desktop-Computer-Dual-Core-PC-2GB-Ram-DVD-Windows-7-Premium-/141161461250?pt=Desktop_PCs&hash=item20dde0f602

Well, the dell is probably an old core2duo or some other two core CPU.

The ebay one would probably be alright.  Seller claims that he's an authorized refurbisher.