Any OBDII will work, but you sometimes have to work the connector on well. The problem is the connector in the Boxster. Some people have been turned away from emmission inspection sites because they just plug it in and it doesn't read anything.
If you want more than just a code reader, go to
http://www.autotap.com and check out their real-time OBDII diagnostics software. It's $180 and I love it. I also have an el cheapo reader/code clearer that I bought on eBay for $25 that works with all of our OBDII cars, including the Boxster.