run a shell script until you want to kill the pid

I was wanting to run an applescript to tunnel to my itunes server using my rsa key from a usb drive. My goal was to run the line until the process is killed by clicking ok. I tried to figure this out by reading the apple technotes 2065 Technical Note TN2065: do shell script in AppleScript, but when I added in lines four and five, the number of the process created on the system did not match the value of pid.

do shell script "ssh -l /Volumes/Mac/.ssh/id_rsa user@ -N -f -L 3689: &> /dev/null & echo $!"
set pid to the result
do shell script "renice +20 -p " & pid
display dialog "End" buttons ["OK"]
if button returned of result is "OK" then
	do shell script "kill " & pid
end if

regards chris

seems to work for me. What pid is it returning - and if it’s different - what process is that?