Could you tell me a little more about what you are trying to do? What devices are you using to generate your signals, and where are you trying to start and stop the aquisition? The way you would go about triggering on a 3rd party oscilloscpe will depend on the triggering options supported by that scope.
If a pure hardware-defined oscilloscope does not give you the kind of triggering you need, you might consider looking into using a NI digitizer. Not only do our digitzers support a large variety of triggering methods, you will be able to choose which samples to display through use of LabVIEW.