It really is very easy import one of the stock models into your editing program such as blender or my personal favourite MilkShape 3D. Then you just need to edit it keeping the width and height the same so its the right size in FPSC. Then you just need to export as a .X file.
You can easily then just copy the FPE files and create the textures you want using something like UV Mapper and there you go you have your segment ready to use in FPSC.
Hope that helps a bit more.
Windows 7 Pro, Intel Core 2 Duo 2.8Ghz, 4GB DDR3, Dual nvidia SLI 9800GT 1GB, 1.5TB Hard disk, OS installed on solid state drive