Start with the image files. I'll assume you have
      both day and night images, as well as a field
      effects file. I don't like to work in the BBW
      folder itself. I get all the relevant files on
      my desktop and work from there, so as to not
      disturb the contents of my BBW folder. I don't
      want to change ANYTHING. I simply want to ADD to
      what's already there. So get your day and night
      images saved as .bmp files on your desktop. They
      should be in a 4:3 aspect ratio in pixel
      measurement. Then you need a pair of existing
      .ini files to copy from another ballpark you
      already have installed. You'll edit these to be
      compatible with your newly-created ballpark.
      Finally, get the field effects file for this
      ballpark and copy it to the desktop. So you'll
      have a total of 5 files with which to work on
      your desktop.

      Yankee Stadium ("New York Bronx 1976-") comes
      with BBW 5.5 so I'll just assume you have it, and
      you can use its corresponding .ini files as a
      starting point. Copy (don't move) the files
      FL-DNYCA.INI and FL-NNYCA.INI to your desktop.

      Get the appropriate field effects file (not the
      one from Yankee Stadium called FE-NYCA.INI but
      the one for the specific ballpark you are
      creating) and copy that file to your desktop as
      well. You should now have all five of your newly
      copied files to work with. You can skip the
      field effects file, as it's not necessary unless
      you want to use field effects while playing games
      at this specific ballpark.

      Close your explorer window that shows C:\BBW just
      to be safe, and now you can start editing and
      manipulating these files on your desktop. First,
      choose a totally unique four-letter, ALL CAPS
      abbreviation for your ballpark. I'll make it
      ABCD just to keep things easy for now. You have
      to rename those .ini files to FL-DABCD.INI and
      FL-NABCD.INI respectively. Then open the files
      individually. Anywhere you see the letters NYCA
      in the file, replace them with ABCD. Also,
      change the name of the ballpark near the top of
      each file to whatever ballpark name you're
      creating. Save and exit notepad in each
      instance. Be sure not to erase "(Night)" from
      the name of the ballpark in the NABCD file. You
      can use whatever name you like. For example, in
      the original files that installed with BBW,
      Yankee Stadium was called "New York Bronx 1976-"
      but I changed it to simply be called Yankee
      Stadium. Also, I have the new ballpark in
      Houston installed, and I call it Enron Field.

Next you have to change the names of your .bmp
      image files. Make sure you can see the file
      extension, because you have to completely get rid
      of the .bmp extension and change it to .dib.
      Having a file with both extensions won't work.
      The day image should be called F-HDABCD.DIB and
      the night image should be called F-HNABCD.DIB.

      Finally, rename your field effects file to
      FE-ABCD.INI and copy all five of these files into
      your BBW folder. If you get a warning message
      asking if you want to replace an existing file or
      files in your BBW folder, click no for all of
      them. You do not want to replace anything. Go
      back to the desktop and start over, choosing a
      different four-letter abbreviation.

      The final step is to open a game in BBW 5.5 using
      your new ballpark, start playing the game as the
      home team (select any micromanager for visitors -
      doesn't matter who), and load the bases with
      intentional walks. You have to move all the
      players and objects around, because they'll be
      scattered all over the place. There are 18
      things to put in the proper location - 9
      defensive players, 4 offensive players, 2
      managers, 2 statistics boxes, the scoreboard, and
      the control panel. Simply hold Ctrl and move
      each item with your mouse pointer. You have to
      hold the left mouse button as well while dragging
      stuff around. Once you get everything where you
      like it, go to Options-Save Ballpark Layout, and
      you're done. You have to repeat this step for
      the night version of your new ballpark as well.