How can I get alt-tab to work in VirtualBox VM when in full screen?

I have VirtualBox installed on Ubuntu 12.04 LTS (host) with Ubuntu 10.04 LTS as a VM (guest). The VM has guest additions installed.

I'd like to be able to reliably use alt-tab to switch windows within the guest, at least when I am in full-screen mode. Instead what I currently get is that sometimes it switches windows in the guest, sometimes it switches windows in the host system, sometimes it activates the HUD in the host and sometimes it does more than one of these three things at the same time.

What can I do so that when I am working on the guest only the guest responds to alt-tab? (I have a similar problem with the super key--though that isn't as much of an issue since 10.04 doesn't make as much use of it.)

Using right Ctrl you can move between real OS and Virtual for the shortcuts. So every time you hit that button, you change between VM and the real machine and there is where the shortcut will apply.

The default desktop that a shortcut applies when you open a VM in full screen is a little bit random. Sometimes inside the VM, sometimes on the real desktop.

You may also want to completely disable the HUD hotkey. I do this because I spent most of my time inside VMs and not on the host desktop.

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