On a virtual lab, assuming that you want to demo this with no physical hardware, I would recommend getting a .pcap of actual WEP traffic (wireshark or tcpdump will do for this) and rebroadcast it with a simple python script or a tool like tcprelay.
Just setup two VMs on the same subnet and use one to broadcast and one to crack. One of the problems that people tend to run into with these demos is that you need network activity on the target access point to get enough data to perform the crack. By doing it once for real (when you generate your .pcap) and just capturing that data off in a .pcap you won't have to worry about setting up some ancillary service to generate traffic for you. It's already done and you will know that there is enough data, very good for demo purposes. Also, I'd recommend using Aircrack-ng over just Aircrack. Aircrack will do but it's kinda out of data.
You should be able to run a similar setup to this on laptop with VirtualBox and two stripped down linux VMs.
Here are some example .pcap files for WEP breaking from http://weplab.sourceforge.net/
You may be able to use the weplab project to get the type of setup you're talking about right out of the box, actually. It looks like they have examples for a number of WEP attacks and pretty good documentation on how to get it all up and running.