I've got allot of experience with low oil pressure and it's causes. Thankfully motorbill was there to guide my path through it all!
Have you tried another gauge yet? They are relativley cheap, (about $15 from the local auto parts store), and it will take all of 10 minutes to hook it up. It will answer allot of questions immediately, and maybe even put your mind to rest if it turns out to be a bad gauge on your dashboard.
In any event, as motorbill wrote, DON'T DRIVE IT until you find out what's going on!
On their death bed, nobody ever said, "Gee I wish I'd spent more time at work!"