hat0112 - Welcome! I'm actually getting married at the Tamarijn on 10/25/10 so it looks like we'll be getting married around the same time! Also, I am orignally from the Philly area, small world!
I would suggest doing ALOT of research on venues before deciding on one. We are having about 20 people as well and the Tamarijn (Aruba Weddings for You) was the best way to go for us, however; people have raved on the boards about the Westin and Marriott as well.
It will seem like so much information at the begining but just be sure to take your time with it all and find the place that's best for you both.
Are you having a reception once you're back home or keeping it all in Aruba?
Good luck!