I know this thread is nearly a year old, but I thought I'd give some pointers and useful links to get started in case other people are interested in 3D modeling.
3DSmax/Gmax are some of the easiest 3D modeling software to learn to use, that being said, they are still very complex, I've been using them for nearly 2 decades and I still have a relatively small understanding of how they work, I tend to keep with the tools and techniques I'm familiar and confortable with. Because they've been around for so long, there are tons of video tutorials online. Unfortunately, Gmax is no longer supported, and 3DSmax is 215$/month.
If you're completely new to 3D modeling, try playing around in
anim8or first, it's free, uses very little space on your drive, is portable (doesn't need to be installed), and is simpler.
SketchUp is extremely simple and especially useful for making buildings and blocky furniture, organic things like plants and animals are trickier to make. The free version only exports to .STL (which will destroy your texture mapping) or COLLADA .DAE format.
LithUnwrap is very useful for mapping textures to models. The version freely available online is the very outdated 1.3 version, the latest version released was 2019, but I missed out on that one and I use version 2017. I'm not sure if I'm allowed to share version 2017
publicly because the program got rebranded as
Ultimate Unwrap 3D and is no longer free.
Blender is free and good to have. I have no idea how it works, but I have it installed and use it to convert models from uncommon file formats (like .DAE) to .OBJ file format.
There is also a
.TPM importer/exporter add-on available. With the fall of Gmax, this is currently the only available, free tool with Trespasser compatibility.
MeshLab is another tool that is free and rather simple. I find it more useful for 3D printing than for game models though. I use it as a model viewer.
Trespasser has extremely small scale compared to most games, I think machf said 1 unit in 3DSmax is equivalent to 1 meter in Trespasser. Most 3D modeling software don't like working with such small models and might not render them properly, so you'll have to scale your models up to work on them, then shrink them back down when you're done before exporting them.
I think Trespasser's poly limit is 2048 per object, but unless the object is a large dinosaur or a building, you should stay way below that. Another thing to keep in mind when modeling for Trespasser is the texture limitations: 8-bit color palette bitmaps with a maximum texture resolution of 256x256. So let's say you're making something like a building with different colored rooms and paintings on the ceiling, à la Hammond's mansion, to have a good level of detail and to not mess up the colors you'll want to assign multiple bitmaps for different parts of the building. Tiling textures can also increase the level of detail without actually increasing the resolution or the number of textures.
Of course, those limitations can be bypassed with CE, but I would still recommend following them in case people want to play with ATX instead.