Process Explorer allows you to search for open files and handles. While I've only ever used it to see which process was locking, say, C:\Vikram\Trades.xls, I *think* it also allows you to search substrings. In other words, searching for J:\ would list the offending processes where J is your external drive. Process Explorer, of course, does much, much more. http://technet.microsoft.com/en-us/sysinternals/bb896653.aspx[^]
Cheers, Vıkram.
"You idiot British surprise me that your generators which grew up after Mid 50s had no brain at all." - Adnan Siddiqi.