Well specwise the Radeon8500 is more powerful, the biggest reason why ATi is cheaper is because they have to be, nVidia owns the market and for them to remain competitive they must appeal to people\'s wallets.
But know this, when going with nVidia never expect good 2d quality, unless you buy expensive quality brands like Leadtek and Elsa for example.
And Tom isn\'t the greatest scource around really, check out
http://www.anandtech.com or
http://www.hardocp.com .
But don\'t try to read those guys console reviews as they are highly biased when it comes to consoles.