The Boxster is completely capable of towing a trailer depending on the weight. I've seen people pull everything from racing trailers to jetskis with a Boxster. You can tow most small trailers, but I would be far more concerned with the tongue weight than the weight of the object. Will Wood recommends not exceeding 750 pounds and 60 pounds tongue, so if you can find a teardrop trailer in that range go for it. If a Mini Cooper can pull a small teardrop trailer I am certain a Boxster can.
Here are some good links:
http://www.bombaydigital.com/boxster/projects/trailer/
http://www.willwoodsystem.com/