You want to go in Safe Mode when removing this. And not go to Normal Mode until you are clean.
The Notify key is in the registry (start-run-regedit) under:
HKLM\Software\Microsoft\Windows NT\CurrentVersion\Winlogon\Notify
Delete the Key on the left which references the bad DLL on the right. Then find and delete the DLL in Explorer.
However, it is possible that this file is referenced in other places in the registry, namely, a service. If so, other such references should be deleted as well.
The problem is that this DLL may not be the "main" baddy, there could be a daddy program that is restarting and renaming it.
So if you delete the Notify entry manually in Safe Mode, and it comes back, you've got some nasties in there which may need more advanced techniques to remove.
If you don't want to edit the registry, then just tell us what IS in the Notify key, and what file it points to on the right-hand side of regedit. Then do a search for that file and post here what other keys it is referenced by.
If all this sounds scary to you, you may just want to take it somewhere to be fixed.