Recently, I was asked to convert all of the 3D assets for TKO (http://www.cartoonnetwork.com/games/cc/tko/index.html) from blender into 3ds Max. The blender files included a master .blend file containing a rigged character and several other files containing actions that referenced it. The end result was to be a master .max file of the rigged and animated character which could be referenced in other max scenes, retextured with additional accessories added to create an assortment of characters. After hours of searching, I discovered that very little information on the subject is available online (although many people have asked!) so I decided to share my solution with all of you. You will need an FBX exporter for Blender (I believe one is included already) and an importer for 3ds Max (I used FBX Importer 2006.11.2 for 3ds Max 8).


Open .blend file in Blender.
Select only the mesh and armature objects you want to convert (shift+click to select multiple objects)
Go to File > Export > Autodesk FBX
In the options box, select:
Selected Objects
Scale: 1.00
Rot X90
Armature
Mesh
Click Export
Save the resulting .fbx

In 3ds Max go to File > Import
Select the .fbx file
In the options box, select:
No Animation
Add to New Scene
Bones > More (make sure Leave as Bones is checked)
Geometry
Skins
Convert the world coordinate to Z
Scale units to m at 1.0 scale factor
Click OK

Some things may need to be cleaned up in Max at this point. Fix any normals that are reversed, smooth the mesh, and make any necessary adjustments to the skin (envelopes and weight). Go to the Materials Editor and fix any materials (there is a known bug in Max’s fbx import that affects material transparency.)

Save the file as .max

In TKO, the animations were stored in multiple .blend files that referenced the master file with the mesh and armature. The following steps explain how to copy all of those animations into the .max file

Back to Blender, open one of the .blend files that contains animation
Append or Link each action from the other animation .blend files so that all of the actions are available to put on the timeline
Open the NLA editor
Select the armature from the left side of the editor
Ensure that snapping is on and set to nearest frame
Add each action to the NLA timeline by pressing shift+A
Make sure each new action starts after the previous action finished (actions that only contain one key may need to be added twice so that the action is keyed at the start and the end of the sequence) I also added a "No Animation" action for the first 2 frames to make attaching additional objects to the model easier later.
In the Buttons panel, under Anim, enter the start and end frames for the entire set of animations
Go to File > Export > Autodesk FBX
In the options box, select:
Scene Objects
Scale: 1.00
Rot X90
Armature
Enable Animation
Current Action
Click Export
Save the resulting .fbx

Back to 3ds Max with the .max file you wish to animate open
Go to File > Import
Select the .fbx file for the animation set
In the options box, select:
Default Take
Exclusive Merge
Bones > More (make sure Leave as Bones is checked)
Animation (in animation details, uncheck all options, and set resampling rate to the framerate used in blender – 25 by default)
Convert the world coordinate to Z
Scale units to m at 1.0 scale factor
Use the FBX file frame rate in 3ds Max
Click OK
Test the animation, and save the .max file.

Should post this on blenderartists.org as well.