If you have got any other dialog box opened, there should be a small arrow on the top right of it. Click on it and choose "Add Dialog" (I think that's what it's called). Now you can choose your layers dialog and you're done.
Maybe it's already opened but you cannot see it? I had that once..
David Wood wrote:Arzorac
Cyrilshark wrote:Argzornack, I still have to congratulate you on having the most epic signature ever. haha