If you really mean "Key to show the HUD", that would never have any effect on the Super key. The HUD and the Dash are different; tapping Alt brings up the HUD, tapping Super brings up the Dash.
That being said, I don't know if there's a way to disable the Super->Dash binding in 12.04; I only have a 12.10 system at the moment, and the settings backend has changed. So unfortunately I can't give you more of an answer.
If you really mean "Key to show the HUD", that would never have any effect on the Super key. The HUD and the Dash are different; tapping Alt brings up the HUD, tapping Super brings up the Dash.
That being said, I don't know if there's a way to disable the Super->Dash binding in 12.04; I only have a 12.10 system at the moment, and the settings backend has changed. So unfortunately I can't give you more of an answer.