PJ
I used a jigsaw fitted with a metal cutting blade to cut the holes in my dash without any problems:
http://www.flickr.com/photos/marlin_...brio/433809216
I used wide masking tape to mark where the various holes needed to be then drilled a hole (large enough for the jig saw blade) in the centre of the part(s) you want to cut out. Its then easy to cut close to the line with the jig saw and finish off with a half round file to neaten up the holes (not that it usually matters as the edge of the instruments cover the edge of the hole anyway).
Simon