Okay, here's all you have to do gwsmith...
Enter the frequencies for a particular net, making sure that the control channel is one of them. See database on this site for that info.
Once those are entered, just hit ID Search and the scanner will sit on the control freq until activity appears and then the scanner will display the talkgroup that's active and the frequency that they're using for that transmission. That's all you need to start hearing something. Write down the talkgroups to build your list and watch the freqs to make sure you have them all programmed. Simple, huh? If you hit SCAN, it will do nothing without some talkgroups programmed so that's why we're going to use ID Search instead. Oh, and make sure you program "trunk" into the scanner, at least for the control freq and mode is NFM, steps are 12.5. Also make sure you have the particular bank you're using programmed for the type trunking system you're trying to listen to.