First off...Welcome Aboard!
In answer to your question there are several ways to do it.
1) If you have Vanishing Point (w/your PS install) you can render a grid in there.
2) Add a new empty layer select the fill (bucket) tool, change it to use a pattern then select a grid pattern (unfortunately I don't have any handy to upload).
I'm sure there are a couple of other ways as well that I'm overlooking.