Conniekat, by decimate do you mean the optimize modifier?

Operaguy, Are you trying to skinwrap the hi-res version to the optimized one?
If so, i would split the mesh in 2 skindrivers so you could morphanimate the low-res and render the high-res and not get a huge filesize and you could use pointcache.
Have you thought of a collada route?
Bring in the meshmorphs{baked} and your animation.
The animation is still editable in max and if you want more control link the skininstance to a biped.
You animate the biped and the mesh "follows" with pretty good weightmaps { the best i have seen of all the "plugin's".