Flexes with 3DS Max
This article contains supplemental notes to Cannonfodder's tutorial on how to create facial animations with VTA files.
First things first. As this is 3DS Max, you are going to need Cannonfodder's 3DS Max Tools. <- Go get 'em.
For the procedure on creating the morph targets read his step-by-step tutorial on HL2World.com. He'll take you through the steps of creating the morph targets, exporting them and setting up the .QC file.
When going through his tutorial I have discovered a pair of things to be kept in mind.
Remember to keep whatever you want to flex animate at a reasonable size. For some reason the vertex animation will not work with things over a certain size. It will only crumble the mesh. I don't know the exact threshold, but my guess is the safest size is that of a human head kept to Valve's scale of a human being 72 units tall.
For some reason any flex animated mesh gets its smoothing groups reset when compiled, resulting in an all smoothed mesh. This means that you cannot have smoothing groups on a mesh that has vertex animation. It is possible to divide your mesh in multiple seperate meshes though that all use the same bones in the Skin modifier.
Example: Seperating head from body, so they are not polygonally attached, both kept as individual objects/meshes still assigned to the same bones. It is then possible to add smoothing groups to the body, while only the head would be reset when flexed on its own.