For starters, check the transmission fluid level and if it's low, fill it to the proper level. Also, there should be a cable linkage between the gear selector and the transmission housing. Make sure the cable linkage is connected and functioning properly. This might require two people, one in the car holding the brake and shifting the transmission and one under the hood watching for proper movement of the cable and linkage.
You say it acts like it's in neutral. So if you don't set the parking brake and/or chock a wheel the car will roll freely, or is it more like it's stuck in park?
-Rod