multiple wirless robots controlled online


I'm new to the arduino-community so I don't know much about all the products and never used them.
For school me and some other guys do a project: multiple robots that fight eachother and can be controlled online.
We will start with two and thought we could use arduino.
what would we need for this project? for one wifi-bot we need 2Xbee's ,1for the computer with a usb-connector and one for the arduino on the bot?
but what for 2? do we need 3Xbee's or 4?
can't the Xbee communicate directly to the pc's network-card?
Sorry if my english is bad,I'm from belgium.

I hope somebody can guide us in the right direction.

If I were you I'd start with plain old radio control and see if you have the resources and knowledge to build the hardware and get something working. Replacing direct radio control with an online interface via Arduino is possible, although I don't see yet how your online 'players' would know what was happening to and around the robot. Are you expecting to provide a video display of the arena, or of the robot's point of view, or something? That would introduce some requirements that would have to be dealt with separately from the Arduino.

We are going to use wireless webcams on the robots that will have to be integrated in the website

Sounds feasible then.

Xbees use a subset of the Zigbee protocol, and this is not compatible with wifi.
They also will only transmit at 115,200 bps max, so are not fast enough to send
video, in case your were thinking of that [I don't think you were].

Another possibility is the Roving Networks RN-XVee module which does use wifi
and will communicate directly with your PC, and which also plugs directly into
the XBee socket.

I've used RN-XVee to setup an adhoc network with my PC, but not yet tried to
go into the main network router, but I think that works too.

RN-XVee operates much faster than XBee, but I don't think it's usable for
transmitting video, either. One problem withRN- XVee is you may have longer
response latencies when going into the wifi network than with using XBee.

not fast enough to send video, in case your were thinking of that

From AnotherEpicName's answer I understood that the video component would be handled directly between the wireless webcam and the PC, not involving the Arduino. In this case the Arduino would only need to act as a wireless controller to move and operate the robot.