just beowulf 100 PS3s together, that should be able to pull it off
Humor aside, I'm afraid some jackass would actually try this. First off, the PS3 doesn't support high-speed networks such as Myrinet or InfiniBand. And secondly, Sony is unlikely to ever provide support for any institution that uses a video game console in this manner, unlike IBM or Cray. I have a blog post specifically about this.