Depends on the DLL, but actual physical position usually doesn't matter, only the path. It's more likely that the 'missing' DLL is only the thin end of the wedge.

Is the DLL actually needed, or a legacy from a bad uninstall? If it's the latter, you could edit it out of the registry - a little risky, but not impossible.

Run 'regedit', then 'find' the file in question, deleting the entries that appear. I say 'entries', because there will be more than one - continue the search until it can't find any more. It's a long process, so brew up before you start!

If it is still needed - the machine won't run without it - you need to be sure the version you have is the right one, and that other files associated with it are also there, which could include VXD or HLP files.

Out of curiosity, what is it called?