Thank you for your response. I don't think it has to be all that complicated. Here is a linkhttp://infinityexists.com/videos/arduino-arp-cop/
to a project that runs a python script to listen to an arp poison monitor. When it recognizes the event it sends a character to the arduino. The arduino then blinks an led.
If a script could be written to poll the bitcoin client/server looking for payment and then send the number of bitcoins to the arduino. The arduino could then trigger (insert anything you can think of here). I wanting to have it turn a stepper motor proportionately in relation to how many bitcoins it recognizes. A candy dispensor for starters.
The arduino wouldn't be running the client, it would only be listening for a number. The arduino is important because I think it is in the spirit of experimentation and open source and widely available. There would have to be a computer attached, possibly an embedded linux system, but at this point any computer for experimentation. Thank you so much for any help.