ZO: Kismac is more for, um, cracking wireless networks, which is handy if you've, er, forgotten your WEP/WPA key for your home network and, uh, need to reclaim it. It supports a variety of methods for cracking passwords. Go on Youtube and type in Kismac.
Neruda: You are correct. However, a) you don't necessarily need to inject packets to crack a network (although it is much easier and faster with injection!) and b) Kismac works with a variety of cheap USB and PCMCIA cards, as well as Airport on older macs.
Kismac development has really stagnated in the last 6 months, which is a real shame. It is far from perfect, and as Neruda mentioned, Atheros support is passive only (no injection) even though there are wireless drivers for eg: Linux which do support injection.
It's a real pisser.
Also, the app is both fugly, and not exactly intuitive to use.