Hey Retardo: [img]/ubbthreads/images/graemlins/smile.gif[/img]
Make a new empy layer on top of your photo.
go to your color palette and pick a nice brown tone.
Use the paintbucket to completely paint the new layer brown, at which point you wont see anything on the screen but a big brown square (as the original layer with the photo is underneath)
Go to the layers pallete and set the layer style to "overlay" and then use the "opacity" slider to make the layer more see through.
You can experiment with different shades of brown, but once you have found the right amount of sepia, you can save it as a custom color, and then just pick it for future reference.
As with a hue and saturation layer, you can select "all" of the colored layer and then just use the hue/saturation slider under "adjustment" to vary the hue to more or less brown as well.
I like this way better than the other suggested way, but like all things in Photoshop, there are probably 50 ways to do it.
And you can use my system to give a color tint to any photo, not just sepia.