This is basicly a quick and dirty compilation of lots of bits and pieces of information about importing the .mesh models of M2 in combination with the use of Vercingetorix's Cas-Im/Exporter to export them again to a .cas model for use in RTW.
As everyone seems to work the other way around (getting Rome units in M2) I couldnt find any straightforward info on topic, where once you have things "lined up" it actually makes perfect sence and there is nothing to it (besides the loss of lots of time!).
First of all I'm taking for granted that you know the tools I'm mentioning in this compilation, if not a decent search will give you plenty of information about the specific tools.
-First of all you need the .mesh models wich you can obtain by unpacking M2's data, how to unpack M2's data is explained in the M2TW-section of this forum.
-You than need to convert these .mesh models to something that can be used, wich basicly means you only have a single option as there is only 1 tool available for this purpose; GrumpyOldMan's .mesh-to-.ms3d converter
The tool is very easy in its use particularly as you only need to option to export mesh to ms3d, wich can be found in the only tab the tool has.
(you can now use the model in Milkshape3d, however as I use 3D-Max I have no interest in Milkshape, next to that you need Max to export to .cas later on.)
-In the case of at least units you'll find they come with several models in 1, so to speak, pick a layer and delete the rest, do have a good look as sometimes certain parts of the models may be different, like the swords on these gothic knights;
-once you have picked a model or just a part you want to import hide it and import a unit from RTW using the .cas importer, use that skeleton/bones and you're already using M2TW-models ... :D