I agree with the previous poster regarding NetStumbler (ww.netstumbler.com)... it's a pretty good (free) application for the MS Windows environment.
In the Linux arena, you can use Kismet (www.kismet.org or net, I think). It does pretty much everything that NetStumbler does, plus it can be set up as a wireless Intrusion Detection System (IDS). With Kismet, you can have one station set as a Master, and other peripheral Slaves that report back to it.
There's (at least one) a Knoppix release that includes a number of wireless tools (including Kismet).
Knoppix (www.knoppix.org) is a Great thing - it's an entire Linux distribution on a CD. You don't have to install it; you just put in the CD and boot it up. It doesn't make any changes to the host drive (unless you want it to) ... when you're done, just shut it down, remove the CD, and reboot.
Knoppix is a good tool all the way around - not just for wireless.
There's also a wireless specific release (I've heard, I don't have it) called "Woppix" ...something like that.
Finally, if you buy a Cisco wireless NIC, the utilities that come with it include a Site Survey tool - it's not much, but it's handy. Basically it's a graph with signal strength displayed on one axis, with signal quality dispayed on the other..... in other words, a 45 degree slope to the upper right corner is a "perfect" signal. The graphical display is very easy to interpret.
Good Luck
Scott
