Forcing a drive to unmount...

If umount /mnt/[driveName] says that device is busy then it means that some process is still accesing the drive..

To check what process is accessing the drive, try
fuser -v /mnt/[driveName]..
In my case, i got

Sorceress:/windows # fuser -v /windows/audio/ USER PID ACCESS COMMAND /windows/audio/ wraith 5854 f.... konqueror root kernel mount /windows/audio

So all i do is kill the konqueror process with a
Kill 5854
and the device umounts successfully

Great source for understanding the /etc/fstab file that has the filesystem configuration information: http://www.tuxfiles.org/linuxhelp/fstab.html