jelect,
What kind of triggering did you want for the mic input on your PDA? did you want to start acquiring when someone starts speaking, or something along those lines? If that's the case, then what you could do is continually call the SI Read.vi and poll to see if the voltage changes by a certain amount. Then, when that happens, do any processing that you need to.
As for the Peak Detector VI, here is the link to a knowledgebase on our website discussing this issue: http://digital.ni.com/public.nsf/websearch/EE144F58DCBE406B86256F1F00669514?OpenDocument
I hope this helps. have a great day!
Tyler S
