The msvcrt10.dll file is only needed for Photoshop CS (all versions, from 1 to 5.1 Extended), because the "new" Photoshop CS filters work in a slightly different way.
If you use Photoshop CS, then you will need to download and copy the eliminate white filter to the ..\plug-in\filters directory, while the msvcrt10.dll filemust be copied in the Photoshop's root directory (something like C:\Program Files\Adobe\Adobe Photoshop CS5.1.
As far as I know, under Windows 7 I didn't need to register the DLL and after re-starting Photoshop CS5.1 the filter worked as expected.
For any older Photoshop version (like 7 and older) the DLL file is not necessary.
Enjoy!