If the themes, color schemes, and font sets that come with PowerPoint 2007 don't meet your needs, you can create your own and then make any combination available to all your presentations as a custom theme.
Masters control the basic design of all slides in a presentation. You can make global changes by editing text and objects on the masters.
To create your own layouts, you can manipulate existing objects on the slide masters. Or you can add an entirely new master and build the layout from scratch.
After setting up a presentation to look the way you want, you can save it as a design template for use as the basis for other presentations.