Hello,
To answer your first question, yes you can use the serial port without a DAQ system. You just need to have the proper drivers for what hardware you are using.
Second, you can use serial, isb, and infrared to communicate between your PDA and hardware. I am including links to our online Knowledge Bases that discuss these options in more detail.
http://digital.ni.com/public.nsf/websearch/11E3697FAC8A0A3786256D44007911BB?OpenDocument
http://digital.ni.com/public.nsf/websearch/15987C8CB752EAD786256DC20070B433?OpenDocument
http://forums.ni.com/ni/board/message?board.id=140&message.id=6288&requireLogin=False
http://forums.ni.com/ni/board/message?board.id=140&message.id=9153&requireLogin=False
Thanks,
Caroline
National Instruments
Thanks,
Caroline Tipton
Data Management Product Manager
National Instruments