Resource Control approach...

[eluser]@li[/eluser]
If you're having users login to your system, store their ID/permissions in the session and use them to gray out the modules they can't see.

If you're listing the modules on a public page (i.e where non-logged in users could also see them), then you should categorize them on user permission levels. I.e Basic members: Show the least restricted modules here here. Plus members: Show some more here. Deluxe members: More here. etc.

That way a basic member will already know he can't access the modules under Plus members level and so on.