in sketchup is automatic
install the right plugin (in attachment)
then create or import the model . then go to the plugin- directx -export model
the plugin automatically exports the texture applied to the model, but you have to be to convert the texture in dds format whit paint.net or gimp
The software I use? ... Autocad, sketchup, Spazio3D, pconplanner, Kerkythea, wings3d, paint.net, torque3d, AxixGameFactory, PD particles.