There are plans afoot to run a 10,000-strong multiplayer beta test for Ms. Splosion Man this summer, with Twisted Pixel's XBLA title to launch later this year.
You'll have until June 12th to sign up, with the beta itself running from June 6th - 24th, and you can sign up here.
There are a few rules and regulations, naturally, but nothing too major. All you need is an Xbox 360 with a HDD, Xbox LIVE Gold, a broadband connection and some time to play with a bunch of other mucky folk over the net. Chances are if you dabble in online multiplayer anyway, you'll be absolutely fine.