If you're having a dif problem, chances are that other people have had the exact same problem. A look through these frequently asked questions could present you with a solution.

General
General questions that pertain to all (or no) modeling applications.

Map2Dif
This section is for Map2Dif.exe specific questions.

Constructor
This section is for Constructor specific questions.

QuArk
This section is for QuArk specific questions.

Hammer/Worldcraft
This section is for Hammer/Worldcraft specific questions.

3D World Studio
Used to be Cartography Shop
This section is for 3D World Studio specific questions.