Apps for quick website mockups? [on hold]

My very realistic bosses want to design a mockup of their next website by the end of tomorrow. It's pretty simple stuff, tabs, menus, faux tables, etc. It only has to be in images atm. Are there any simple tools I could use to get the job done quickly? The only other time I did them was in css was a bare html page. I do have PS.

thanks!