Making menu item unselectable

["no6 pobox com" <number6 ip120 gte16 rb1 bel nwlink com>]

How do I make a menu item that appears on a menu not selectable?  I want
it to be in that half visable, grayed out state, but you can't select
that menu item. I also need to be able to change its state back to
selectable.  There must be a property that controls this, but I can't seem
to find it.

Thanks,
Adam
---
Adam Bernstein   no6 pobox com   http://mpgedit.org/~number6
"Who are you?  The new Number 2.  Who is Number 1?  You are, Number 6.
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