I use a 960 gridder layer. You can pick it up at http://960.gs (it's the very top left "download") That will have all the files you need.

Basically you lay it over your PSD (it's just a folder with layers), and it will show you where the gutters are and the columns are. If you've never used a grid system it's very confusing at first, but I feel like it paid off in the long run.

Alternatively, you can slice your entire template. Which is something I used to do... It makes everything an image which kind of sucks. But photoshop will save it as an html table, which makes it a lot easier than using 960gs. I wouldn't consider this method very good at all, but give it a try because it might be useful for some things. It's something like file > save for web > slices or something XD