Wall Worm Anvil
Formerly called Wall Worm Displacement Tool
Understanding Displacement Blend Texture Scale
This page explains one cause for displacement materials to be scaled incorrectly in Source as well as the solution. You should use bitmaps of equal dimensions in both materials controlling the Blend material.
Brush Geometry, 3D Skybox, 2D Sky, Animated Textures
Video tutorial and sample file on exporting a 3ds Max scene into a Source VMF file with Wall Worm.