Hello and welcome to the forums.
Right now Game Guru does except static .3ds meshes, but there are a few issues. Static FBX files of certain flavors, and x files static and animated.
After the Direct x11 update then Lee will be refining the import module to be mainly FBX based. This is still a WIP at the moment. Details can be read here:
https://forum.game-guru.com/thread/218038
There are a number of 3rd party programs that can convert meshes to the x file format. The best one is Fragmotion. Import your mesh in which ever format you have and export it to x file. Fragmotion has a demo version with full capabilities.
Another program is Blender. This is a fully functional free program that will convert meshes to x file format also.
There are a number of threads talking about both programs.
Use the search button above right and type in the name of the program and see what comes up.
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, Screen resolution 1680 x 1050.