There is much more involved than just marking off a 25X75 section of land. How would the loss of the land effect the value of your neighbors property? How much would it devalue his parcell to cut it off and give it to you? A fair price to whom?
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.
You will have to negotiate with the owner of that piece of property and once a price is agreed upon, you must have it surveyed and do a lot line adjustment per your counties requirements. This must be done so that it is registered with the county and it is permantly attached to documents with both parcels.
if agreeable by all parties as to size and price you would need to connect with a licensed civil engineer to draw up the description to be conveyed. After this either the Title Department of the Title Company or perhaps an attorney my be able to finish the transaction.