How to attach an .mdf file that was not properly detached?
It sounds like the database is corrupt. Before you do anything further, make a copy of the files, and only work with copies.

You might try the following, in case the problem is isolated to the log:

CREATE DATABASE [GRMStemp]
  ON (FILENAME = 'c:\wherever\MDF_File.mdf')
  FOR ATTACH_REBUILD_LOG;


If that fails, there is a forum post on MSDN by Paul Randal which describes a process that might work. Basically:


on your 2008 instance, create a database with a data file of the
exact same size (I wouldn't bother trying to put a 2000 instance
anywhere)
shutdown SQL Server
rename the new database's mdf file, and paste the old one in its place
bring up the server and let the database attempt to be recovered and then go into suspect mode
put the database into emergency mode with ALTER DATABASE GRMStemp SET EMERGENCY;
run DBCC CHECKDB (GRMStemp, REPAIR_ALLOW_DATA_LOSS); which will rebuild the log and run full repair


BTW If the client has no idea what was in the database, and wasn't responsible enough to maintain proper backups, how important could the data be?