If you want to increase performances in Warcraft 3 or You have problems with DirectX You can run Warcraft 3 in OpenGL mode.
OpenGL for Warcraft 3 is used in Linux and OS X and it can be used in Windows.
To run Warcraft 3 in OpenGL mode right click on Warcraft 3 shortcut and in Target field ad "-opengl" tag (without quotes).
Target field should look like this:
"C:\Program Files\Warcraft III\Warcraft III.exe" -opengl