There should be no penalty for a div overlay - it's a common technique on today's websites. However, the text in the overlay will shift the balance of your page and it might be ranked differently because of that. This could be either positive or negative.
It's cloaking if you don't show the same source code to googlebot as you do to other user-agents. Even then, there cane be "edge cases" - and as long as the intention isn't deceptive, it's usually OK. For example, Google usually is OK with short extra messages being added based on the referrer.