Darren,

I don't think there is any significant difference in accuracy between an analog polygraph device and a digital (computerized) device.  Keep in mind that both are built around the same flawed theories and the results of both are up to interpretation of and manipulation by the examiner.

I think the questioning scenarios will depend upon the circumstances under which you are being examined.  If it happens to be for pre-employment screening for law enforcement or intelligence positions, check out some of the literature available at this site.  Otherwise, I think there is a good chance that you will see all three types of questions - relevant, control and irrelevant.  Note that control and irrelevant questions are not the same and serve different purposes.  I recommend you read The Lie Behind the Lie Detector if you absolutely must submit to a polygaph exam.