my son has a 1995 Z28 i think he has a weak oil pump it sits at around 40 but when she warms up goes to zero but when you set on the gas it goes back up.
He comes home from Iraq in a week then gets block leave for almost 30 days was wondering how hard it would be for us to change it.

 

Oil pumps rarely fail on their own. How many miles are on this car? You should get a mechanical oil pressure gauge and verify that the readings you are seeing are true readings. It is more likely that rebuild time is right around the corner.

 

147k but he had the top half done before he went to Iraq.

 

If by "top half" you mean the heads/intake, that really won't have anything to do with oil pressure. Oil pressure is an indication of the health of your main, rod, and cam bearings.