What !Bang command should I use with WIN + D to make it just like the key combination in Windows XP?

WIN+D to show desktop (minimize all windows)
and then
WIN+D again to restore all windows to their previous locations.

!MinimizeWindows and !RestoreWindows is not the same...

My hotkey.rc states:
;--> These were setup to mimic the hotkeys available in the explorer shell
; Please note that the hotkeys are defined based on those in xP

so I assume it can be done

/senter

Use showdesk.dll.

where do I find it?

the same place you can find almost every single litestep module. http://www.loose-screws.com

or in http://shellfront.org/modules-list.php