How to Make a 12 Column Grid in Illustrator
05.25.2011
file > new > 1500px by 1500px art board
Rectangle tool > 920px by 1200px
rectangle tool > 880px by 1160px
ctrl + a to select all > window > align > click horizontal align center > Click vertical align center
select inner rectangle > Object > path > Split into grid > Number 12, width 55, gutter 20 > ok
ctrl + a to select all > view > guides > make guides
for a 960 pixel layout use these dimensions:
outer rectangle 960 x 1200
inner rectangle 940 x 1180
grid number 12, width 60, gutter 20
ctrl + ; to hide guides