Using MDF, NDF & LDF is really historical and convention more than anything else, it does however allow the files to be easily identified as database files. When you move the log file to the log drive you can rename the physical file, including the file extension(s) as shown below.

ALTER DATABASE MyDatabase

SET OFFLINE;

GO

-- for mdf

ALTER DATABASE MyDatabase

MODIFY FILE (NAME='MyDatabase', FILENAME='H:\Data\MSSQL.3\MSSQL\Data\MyDatabase.mdf');

GO

-- for ldf

ALTER DATABASE MyDatabase

MODIFY FILE (NAME='MyDatabase_Log', FILENAME='H:\Data\MSSQL.3\MSSQL\Data\MyDatabase_log.ldf');

GO

-- Move and rename the physical files before the next step as appropriate

ALTER DATABASE MyDatabase

SET ONLINE;

GO

Cheers

Leo