Can give you a few pointers that might help here.

What software to use.... this is a tricky thing. There are several issues here to overcome, starting with getting the models OUT of RTW to mess about with. For this, you need G-Max or 3DS Max. Once you have the basic skeletons outline and proportions sorted out, you can make new models around this outline.

I personally don't like modelling in Max for low poly applications ( and RTW is low polygon in 3D modelling terms ). It's over complicated and fiddly to use. This means I have some knowledge of format swapping!

First thing I did was to export a set of skeleton outlines form Max. These were made by placing a small cube on EVERY joint in the model, with some thin triangles joining them up. These were then exported in 3DS format. 3DS is an IDEAL format for messing about with, since just about EVERY piece of 3D software ever will read it in and export it too. Including Max.

With my skeleton outlines, I can make sure EVERY model I build elsewhere is correctly proportioned to fit well over a stock RTW skeleton, and helps to make sure that the scale will be right too. Even if I screw up the scale, the Max scale tool set to uniform scale all dimensions will sort it out.

IF you find you need to mess about with file formats, then a program like 3D Exploration is an invaluable tool. IT opens and saves just about any model format you care to mention. IF you don;t want to model in Max, then something like this can really get you out of trouble.... but it assumes you are familiar with a piece of software incompatable with Max's available plugins for model import. ..... like me....who models in Lightwave. There is NO suitable LWO import plugin for Max.

Does this help any?

Once you have something like my skeleton outlines, you can vuild your mesh and texture it ANYWHERE and just use Max as a final conversion tool.

So...what to choose....

There are several cheap / free options available here. Go with whatever you feel happy with, just so long as it can export 3DS. This includes software like Anim8or, Blender and cheap options like AC3D or Milkshape 3D. There are others ... like 3D Canvas.

Make sure :

1) It exports 3DS format WITH TEXTURES
2) You can properly UV map
3) It is well documented and easy to work with

Then....when you are confident that you have made some models you REALLY want to have in game, download the MAx demo, and convert away! Import your textured 3D models in 3DS format, and you will be good to go.