Before you begin, you need a system that is capable of not only running Snort, but also acting as a wireless access point. The cheapest way to do this is with the venerable Linksys WRT54G wireless router [reviewed here]. The WRT54G runs open source firmware that can be replaced with many alternative distros that offer enhanced capabilities - including running Snort. Alternatively, if you have a spare machine, a wireless card, a normal Ethernet adaptor, and a lot of spare time, you can set it up as an access point.
Figure 3: Linksys WRT54G
This article will use examples using a WRT54G router running OpenWRT RC 2 (codenamed 'White Russian'). There are many Linux distributions for wireless routers available (something I hope to cover in a future article), but I chose OpenWRT because it is simple, lightweight, and comes with a package system similar to Debian Linux.
Figure 4: OpenWRT in action
(Click image to enlarge)