Well I hate to say it, but it sounds like the ignition switch. Theres almost nothing else that would cause the gauges to dance around like that. There are a few other things that would make it not start, or even not crank, but that dancing gauges is pretty typical of an ignition switch.
Now what you can try doing, if youre feeling really adventurous, is to take your own ignition switch out, and clean up the external contacts. Several members, myself included, have had luck with that.
I did an instructional post on the removal here:
http://www.automotiveforums.com/vbul...d.php?t=736656
I think if youve got some confidence, common sense, and a basic set of hand tools, you can do it. Oh, and add patience to that list.
Ignition switch problems are pretty common around here, computer problems are not, take that with the usual grain of salt.
Also, does the Security light blink when it wont crank? Do you have a Service Engine Soon light on when the engine is running?