Hi,
Sorry to dig up this thread.
Just a bit of info which I picked up from the same place you got your original schematic ( http://www.arduino.cc/cgi-bin/yabb2/YaBB.pl?num=1187962258 )
People discovered that the circuit worked better without the 100K resistor (or any thing for that matter) connected to pin 6 of the opto-coupler.
I tried the same circuit with and without. The circuit didn't work with the resistor but worked perfectly without.
So just to reiterate, leave both pin3 and pin6 open.
Let us know how the project is going.
Cheers,
Col