Mae, sounds like you are looking at the Champions Race. Ignore that, it doesn't really mean anything right now. Look at the Entry Rankings, that's the one that is used for tournament entries and for seedings at tournaments, and those are the 'points he has to defend.' It will be updated later on today when all tournaments (including Challengers) have finished and posted their final results to the ATP offices.
This week, Tommy earned 175 points for winning Delray, and I don't think he lost any since he didn't play last year. He is 30th in the rankings this week, and this win could move him up to about 26 or 27 (depending on the points of the other guys around him. I always underestimate).
This page might help you a little bit (or confuse you even more, hard to say
).
http://stevegtennis.com/rankings/2006/s013006.htm