convert a 960 grid based site to responsive

convert a 960 grid based site to responsive

the website i designed (www.aim.ca) is using nathan smith's 960 grid. i
wanted to convert the site to responsive and so i've looked into the 996
grid (responsive) system. http://996grid.com/
in the process of implementing the css scripts and javascript, i had
encountered some setbacks... this is actually my first time using a
responsive grid system.
my questions are: - should i also modify the div classes and ids of my
separate stylesheet to be responsive as well?
when i resize the browser, the elements are out of proportion, i also see
random numbers that i think was generated from the js like "389" and so on
can i modify the 960.css itself using media queries? how hard would this be?
what is the best way to convert a 960 grid based site to a responsive layout?
your thoughts are greatly appreciated! thank you in advance.