In Windows, I often use the keyboard commands to navigate through the menus in a program. For example, in Photoshop, I can do Alt+F, then D to quickly Save for Web & Devices. Or Alt+V, then D to Clear Guides. This is great when there is no keyboard command for a menu item that I want to use, or the existing keyboard command requires too many fingers.
How can I translate this functionality to OS X (OS X 10.5.8 in case it matters)? How can I navigation through an applications's menus using keyboard commands?