I have a question about loading 3ds using this tutorial. I want to use more than one texture on the model (because here all the models have more than one) but it seems that this library can't do that. Do you know any other alternatives or a way to edit this existing library to reach my aim?
You can make use of AssImp.
It's a fairly comprehensive library with importing code already written for you and even provides a sample C++ OpenGL program here.
Well I don't know, but if you read a little the documentation of the file format, it should not be that hard, since the space simulator done the most part for you, you just need to tweak a little the code to add support for this.
You can find a lot about the 3DS File format googling it
Also, here's a search made for you: http://the-labs.com/Blender/3DS-details.html
I think the relevant part for you is at the chunks 4140H, 4170H, A200H(Maybe), F140H(For animations)
Good luck :D