Thanks, your second suggestion inspired me to stop the sql service, ensure i had multiple additional copies of the mdf/ldf files and rename the originals to keep them out of the way when i restarted the sql service. Don't know why i didn't think of that in the first place.
so, on with the restore....
restore detected an error in database 'sims' as read from the backup set.
oh well.. lots of older backups to try...