[casual_games] Casual Games audience hardware survey ?

[Murat Aktihanoglu]

I need rough numbers to estimate how much of an audience I would be 
shutting out if I required users to have a vertex AND pixel-shader 
capable graphics card to play my game.

There is:
http://www.steampowered.com/status/survey.html
but this is a survey of Valve-customers who are not exactly casual 
gamers. Any input is greatly appreciated.

cheers,
Murat