If I get into beta, my first thng will be to smith a crossbow and fight a legendary dragon. 
This isn't really the point of the beta, I daresay. While I'm not saying you shouldn't have fun, what Bethesda wants and needs from beta testers is a careful anolysis of what they've created, people who will search constantly for bugs, glitches, or things they just missed, and report them to Bethesda so they can be fixed in time for the true release, so everyone can enjoy a version of Dawnguard that's as bug-free as possible. You can still have fun, but thinking "oh man it would be so cool to do such and such if I'm in the beta" will only bring a greater disappointment if you don't make it.
Correct me if I'm wrong though.