Have you read all that this feller has written?
http://s3d.skwas.com/
That's the defacto standard of import / export for SH4 models. You have to export files from your 3d drawing app in the only format that S3ditor understands... I just barely have figured out how to view and move the models in it's viewer in the almost 10 years that I've been noodling with it, so I'm not one to advise on procedures there, but look over there and on SubSim for the same program. Lots of reference material... It aint' easy to get the hang of I'm sure, but there are folks with a ~LOT~ of talent hanging around here to ask questions of...