Greg brings up some good points. Here are a few more things you will have to find out-if the 25 x 75 piece is deeded separately from your neighbor's main property then the process will be much easier. If it is all included in one deed,, then your neighbor may have to seek a minor subdivision approval from the town. If the reduction in size will make your neighbor's lot non-conforming he will not be able to subdivide Do your homework and talk with your local zoning officer so that you know what will be required of you and your neighbor. You will not need a Realtor, but please be sure to use an experienced real estate attorney. Good luck.