The secondlife protocol bug is fixed long time ago aint it?
Either way, as in any hacking situation. Go for the easiest target, if you are just doing it to get access anyway.
And, dont think of it as a game or a website. Its all servers and services. Website being one of the services.
Now, to get things clear. Is the secondlife thingy a browser plugin like flash or is it a executable you run on your computer and you login from there?
Either way, get an understaind og protocol fuzzing and manipulation. Find what type of info is being sent back and forth from you and the server and take it from there.
Really, I cant help you a whole lot more, you just have to know the basics of penetration testing.