In asking about Transact-SQL, you are referring to the language and not some kind of IDE, correct? Multi-Edit has language support for SQL and PL_SQL. Have you tried associating the file extensions for your files to one or both of these? It may be that Transact-SQL is different enough that you will need to add some things to one or the other of these already existing languages that are currently supported by Multi-Edit.
More information on adding language support can be found at these two links:
http://www.multieditsoftware.com/TheDev … 04.htm#CLH
For a basic understanding to get you started.
For a much more in-depth and expansive technical article on the process of adding language support.