Hi. I came across this message since I've also had trouble with iStumbler on 10.6, but meanwhile I have something of a solution to the original problem. As mentioned, dropping wireless connections seems kind of an old problem - I had it on an older Mac, too, until I found the solution.
I
think Mac would describe this as a feature rather than a bug - as I understand it, the deal is that wireless connections take battery power, and so they drop
unused connections for you when on battery power, to save juice. Feature!
If so, that's why iStumbler worked - it kept "pinging" the network, which kept your connection in-use. But another solution is to use the very simple "ping" program in a terminal. So open a terminal (in spotlight you can type in 'terminal' and choose that application) and in the terminal type something like this:
ping google.com
This will send a continuous little "ping" message to Google, which Google politely returns, usually in mere milliseconds. Keep this running in the background to keep your connection live. Of course you can ping many other major sites besides Google.
The ping program also gives you some handy information about how healthy your connection is (which was its original purpose). To stop the "ping" you can always hit ^C, or just exit from terminal.
Hope this helps.
