KellyK posted a link to a good thread, check it out. But since your oil pressure is going to zero, it's very likely your oil pressure sender is going bad. No worries, it's just screwed into the block, next to the oil pressure sender. Your local Autozone will have one (or can get you one) and it's both inexpensive and very easily swapped. It'll be the doo-dad with the wire connection on it.