Firstly, not sure where exactly this should go (feel free to move it! but please tell me where it goes if its moved).
Programs (hopefully only these): explorer, notepad, command prompt.
Wished filetype (if possbile): bat or scf (possibly exe).

Okay, so I am sure you are all aware of what 'Show Desktop' does: what I want to achieve is a button that minimizes all windows (shows desktop) and then brings one particular executable (which can be alt-tabbed to) to the foreground. I've given this a go, and asked around with my techie friends and they hit a brick wall as well. Not sure where to go from here so I came here.
OS is xp (64 bit).
The purpose for this is to have a clock that "stays on top" of the desktop without intruding other windows :)
Thanks in advance! 

Winkey+M - minimise desktop.
Alt+Tab - open any running application.

You have a clock in the Notification Area always visible.

Not that I know of. But as you can only be active on one window at a time, using Alt+Tab isn't going to be any different to all windows being displayed.