CSS 960 layout question

Hi,

I'm having an issue and was wondering how to solve it.

I want to use a 960px center layout (I'm using 960.gs) however I want a right hand border at 620px right of the center position going right to the edge of the browser.

How do I do that? Basically I want the grey area somehow to be definable (so I could create a different color background for that part of the screen) -

http://g33.org/how.png


Thanks,

Gary