I really enjoyed the your use of the chamber...I always thought that harry could've of used a secret place only he could access a bit more...
Storywise, I think it was a very intriguing beginning, but there were a few parts that seemed a bit rushed and could've been fleshed out a bit more over a few chapters (ie. Harry becoming more powerful, him instantly trusting Daphne rather than just letting her hide in the chamber, meeting the magical snake/basilisk, etc). I feel that would've given the story some more depth.
Overall, its a very promising and intriguing beginning and I look forward to the next chapter!
Ps. As for animagus forms, I always thought Harry would've been an excellent bird of prey (an hawk/eagle) w/his love of flying...not so sure about Daphne as there is very little info available about her.