UPDATE 26/10/2011 Added support for night vertex colors.
UPDATE 01/11/2011: Zoom extents after import, autodelete of isolated vertices.

Night vertex color and alpha are imported to mapping channels 3 and 4 (x-coordinate only) respectively; let me know if you are able to view and edit the information.

Instructions

In addition to 3ds max you need to have .NET framework 4 and Max.NET installed.
You will also need Kam's gta_material.ms which is included with his scripts.

Download the Max.NET installer here.
http://www.ephere.com/autodesk/max/downloads.html

Download Kam's 3ds max scripts here.
http://www.gtagarage.com/mods/show.php?id=9172

But it's important to note that the plugin will not work with versions prior to 3ds max 9 since they do not have in-built support for the .NET framework.

Copy GTADffImporter.dll into <3ds max root folder>\plugins. It's advisable to run 3ds max as administrator; sometimes it didn't work when this step was omitted.

The plugin is accessible from the utilities tab: Expand the "Utilities" rollout and click the "More... " button. In the list you should find an entry for "GTA DFF importer".

The utility brings up a dialog. Click the "open" button to choose a file. One or more numbers will appear in the listbox; these represent clumps in the .dff file. The numbers are the offsets(i.e addresses) of the clumps relative to the beginning of the file. Select one of them and click the "Import" button to perform the import.

Most .dffs are single clump.

Features

Imports GTA III, Vice City and GTA SA models.
Imports materials, normals, both UV maps and vertex colors.
Limited support for peds: mesh is imported but bones are represented by dummy nodes.
UV and other animations not supported.
2dfx not supported.
Does not import collision data.