Tapping Alt places focus on the menus.
Tapping on ALT is also used when adjusting camera focus, and to display physical or scripted objects. This has been causing problems for people using the first look viewer already.
This is the second or third iteration of your experiments with focus on the menus, and I'm still not sure why you're implementing it in the first place. It exists in Windows to allow you to operate applications without a mouse, but since SL requires a mouse to operate this is hardly a critical feature.
Where did you get the requirement for this feature from? Is it on the BLOTTD, do you have users requesting it, or did someone just think it's a good idea?
PS: if you REALLY want to emulate Windows, you could use alt-space to focus on the menus, since that's how Windows focuses on the command menu and it's a common way to get into the menus to begin with.