<p>I have a Microsoft keyboard with a series of non-standard buttons such as "Mail", "Search" , "Web/Home" etc.</p>

<p>It would be nice to be able to bind these keys so they execute arbitrary programs.</p>

<p>Does anybody know how to do this in Debian Etch?</p>

I can't say for certain because I'm not using Debian but if you're using Gnome the easiest way is to run gnome-keybinding-properties (System > Preferences > Keyboard Shortcuts)
Instead of typing a shortcut such as
Ctrl
+
M
, hit the button on your keyboard.
If you would prefer to do this via command line or with a different desktop environment, this may help:
Unusual keys and keyboards