The low oil pressure light means exactly that, your engine's oil pressure is low. First off stop the engine and check the oil level after about 5 mins to let the oil drain back into the oil pan and get an accurate reading. See if you are low on oil. If you are top it off to the full mark. If your oil level is fine, and the oil pressure light is coming on, your oil pump may be going out, I find it hard to believe that with it being a 2004 that you have that many miles on it to tell you that the engine may need rebuilding BUT if the engine's maintenance has been neglected and no one has changed the oil and filter, the dirty oil circulating through the engine can cause your bearings to wear out warranting a rebuild. Let's hope it's just a case of either low oil or the oil pump is going out.