Multiple Arduinos on One Receiver

Hello guys,
I'm in to arduino for like 2 months now.
I have done couple of little projects.. Not big things..
But I've been asked to do a little more bigger project.
The project consist of about 100 fsr pressure sensors.. Fsr sensors will be in bulks of 5..
The main idea is;
We will have 20 tables and each table will have 5 chairs around it.
We want to count all the sittings.. For example in the end of the event, table 1 will have 45 sit counts, table 2 will have 72, etc..

So I planned to do this project like this;
I will set up one arduino for each table.. Every arduino will have 5 fsr sensors and one xbee wireless transmitter connected to it.
And when someone sits on a chair, the arduino will transfer id of the chair and it's own id to the main receiver arduino..
Receiver arduino will write this data to a table..
Like:
Table 1 - Chair 2 - Time: 16:52 09.07.2012

I can to this kind of fsr sensor data transfer with one arduino with usb connection.
But I do not know about wireless connections or any capabilities of it( 20 clients - 1 server? )

I kindly request your help for this wireless system approach, or any ideas you have about a different point of view..

Thank you in advance..

I would set it up as a master that queries the 20 tables for their status, thus you do not have 20 transmitters all going at once.

Is the point to count how many people or how many times they sit down and get up. I might get out of my chair 3 times during a meal...

@mcreefer,
Need to go events with more attention grabbing speakers!

@CrossRoads

I was thinking more on the lines of taking ritalin. LOL.