Select options in pop up windows

Something has been driving me nuts for ages.

When you close any document, for example, and the mini window drops down to ask if you want to save, how do you change the option without the mouse.

I've tried tab key but it doesn't do anything. There must be a way, these boxes appear for loads of functions so there must be a keyboard shortcut.

If there is a blue button (the default answer) use return to select that. If there is a button with a blue border or ring around it use spacebar to select that. If there's a cancel button cmd+. will activate that choice.

There are some apps that weren't written to use these correctly but most are.

Esc will always cancel a dialogue which is easier to remember and activate than cmd+

LiteSwitch is a free utility that does this in OS 9/Classic but it was never ported to X. Could this be done with an Applescript?

Often you can also select options by the first letter of the option, i.e. hit 'd' to select 'Don't save' or 's' for 'save'.

True.