Okay, I am having a massive outdoor party..Here is my plan for the music. My Mac Pro will be down stairs that has my iTunes songs on it. I have an Airport Extreme for my router.

Now, I will have one set of speakers in the back connected with an Airport Express for the music. I will have another set of speakers in the front also connected with an Airport Express using Airtunes.

I will be controlling the Music with an iPhone and iPod Touch. My main question is my Airport Extreme doesnt cover where I would like to control the music from, So does the Airport Express also extend the wireless signal while being used for Airtunes?

Please answer ASAP.
Thanks