As an alternative to Photoshop and Markup you should also try my app, jMockups [1], a web based high fidelity mockup tool. I launched it on HackerNews about a month ago [2] and you can already mockup most existing sites with it. You could create the mockup in this tutorial in about 10 minutes (complete with the gradients and 960gs integration). If I wasn't on vacation and using my iPhone at the moment, I'd show you :)
I really do need to get some examples up there...