How do I prevent Ubuntu from capturing the Alt key to show the HUD? [duplicate]

Possible Duplicate:
How do I modify or disable the HUD's use of the Alt key?

When I press ALT key on virtualbox machine (ex XP), ubuntu 12.04 catch that key.

How to prevent ubuntu catch ALT key?

Thank you~

Disabling the Alt key from showing the HUD:

• Install CCSM with sudo apt-get install compizconfig-settings-manager

  

• Start it from the Dash or by typing ccsm from the terminal.

• Type "Unity" in the filter box on the left, and click on the Ubuntu Unity Plugin:

  

• Click on the <Alt> button the red arrow points to, and then uncheck the Enabled box. Click OK and close CCSM -- the Alt shortcut is now disabled.

• If you no longer need CCSM, please consider uninstalling it.