Inset lines can really be a cool effect on your designs and interfaces. Here I will show you how to make them
Start with opening your image.
Select the Singel Row Marquee Tool. (To select the Singel row marquee tool just left click and hold down the mousebutton until the alternative selections are shown like in fig. 1. Then select the wanted tool...)

Place the singel maquee tool on your image. If you want to move the selection just use the arrow keys. One touch at the arrowkeys = 1 pixel.
Your image should look something like this

Create a new layer.
Make black your foreground colour and select the Paintbucket Tool. Fill your selection with black.
Now create a new layer. Make white your foreground colour and fill the selection with white.
Deselect.
Your image should now look like this

Select the Move Tool.
Now move the white line 1 pixel down by pressing the down arrow key once.
Change the layer mode from Normal to Soft Light.
Your finished! Your image should look like this

This will be useful in your designs, and by adding some shadow effects that will be great :) have fun!!