MB-A creates a library on a drive accessible from both machines, add links to the files and playlists (the playlists need only exist in the Playlists sub-folder of where the library is located, so can be copied using windows explorer if thats easier)
Exit MB-A
on MB-B create a library, but use the option to choose an existing one ie. the one you just created on the shared drive
some catches:
if you are using a drive letter mapping for the share, you need to make sure its the same drive letter on both machines or alternatively use the "run as a portable application" which doesnt store file links with drive letters,
or instead of using a drive letter use a network share \\xxxxx\yyy when adding the files to the library