Examples: 1.Before I go on a holiday, I usually book my accomodation in advance. 2. I try to get to the air port well ahead of time, so that I don't miss my flight. 3. I check all my luggage beforehand and tie a bright ribbon on the suitcase.

Basically the same meaning. However, you would only say, "Thanks in advance"--you wouldn't say "Thanks beforehand" or "Thanks ahead of time."