The idiotic user agent based restrictions put in place by Hulu are annoying and have led to some creative solutions. The most common involves using your PC to act as a go between Hulu and your device. While there are more expensive solutions using Splashtop, PlayOn, or others Daniel Bingham has created his own take. Luhu performs the same function by streaming videos onto your Windows Vista or Windows 7 PC and then transcoding it to your PlayBook. There are quite a few caveats such as needing a fast PC and no video controls but it is a start.
You can find Luhu in App World for $1.99. I highly recommend reading Daniels post on the limitations of Luhu on his website along with the video below that shows how it works: