You can use any program that will export xfile format.
3D MAx, static and animated, great program, coast a bunch of money
Maya, Static only , animated thru FBX thru another program. a bunch of money
Blender, static and animated, Free,
Fragmotion, free and paid, people have been using this for years. I use it on stubborn models to correct eh xfile.
a host of others that are to numerous to list completely. The main thing is does it export X file.
Photoshop with the NVidia dds plugin. great tool, costs money.
Gimp and the .dds and Normal plugin. Great tool and free.
Changing camera for fine tuning of placement:
Left mouse button (LMB) on an object and press propertied. You can now move around the insert point (That white sphere) from any direction and use the arrow navigation keys to move and object. Pg up and Pg down for height. Holding control and these keys enter fine tune mode.
it takes about a half hour to get the hang of navigation and placement options. The is also F9 mode when in test game.
Hope this gets you started. and thanks for posting. There are guides on the steam board, in the community Hub, with instructions on different parts of creating and editing objects.
Intel(R) Core(TM)2 Quad CPU Q6600 @ 2.40GHz, 2400 Mhz, 4 Core(s), 4 Logical Processor(s), 8gb RAM, Nvidia gtx660, Windows 7 Pro 64bit