Creating a 960px width

[Simon Davies]

I thought the site or the examples go on about is a 960px site, but the 
examples and the code all come out as 1120px wide, how can i make it so my 
site is 960px width and not 1120px width what do i need to 
amend? Probably have to set it to 980px as the 20px guttering so my 
graphics fits my actual size 

thanks in advacne