I use this:
http://technet.microsoft.com/en-us/s.../bb896653.aspx
to work out what is using the DLL. Run it and click on "Find" at the top - type in the DLL name. With luck, it may be a process (or two) you can kill, allowing you to delete the DLL. Failing that, you may be able to delete the file on boot using this:
http://technet.microsoft.com/en-us/s.../bb897556.aspx
I tried it once but didn't have a lot of luck - that may have been because I was working on a Windows 2000 PC (heavily wrecked - mucho spyware. Now sorted).