If you want to stream both the audio and video from your macbook pro, then you are going to need an AppleTV instead of the airport express. The airport express does not do video directly.
Since both devices are the same price you may be able to exchange a new express for a new appleTV.
The primary catch is that your MacBook Pro has to be an early 2011 model or newer to support airplay mirroring.
If you go to support.apple.com/kb/HT4132 you can find out what model you have.
A simple test is if your Mac supports AirPlay mirroring, an AirPlay mirroring icon appears in the menu bar when an AppleTV is on the same network.
Assuming that you MacBook Pro supports it, and you get an AppleTV and place the two units on the same wireless network:
You select the airplay mirroring icon (looks like an up-arrow in a box) and select the AppleTV, The icon should turn blue.
All you then have to do is connect the audio and video outputs from the appleTV to your projector and speakers. You'll probably need the proper cables to do this so check to see whats needed.
You should be all set after that.