Video tutorial (OUTDATED, version 7.1)HERE, or text tutorial below.
Movie maker rendered it impossible to read the stuff, but you should be able to get the gist with this tutorial.
Tutorial for Sketchup Free version 8.0
1: With your model open in sketchup, go to file/export/3D model and make sure the dropdown menu says collada/.dae. Hit export. Now, go to the file you exported them to.
2: Sketchup exports textures as texture1, texture2, etcetera, so we need to fix that. Open up the .dae file in a text editor, go to the bottom, and where it lists the textures replace texture0, texture1, etc. Now, go back to the folder and open up the .tga files and rename them to what you want, then replace the names in the .dae with those of your textures.
3: Open XSI Modtool and go to file/crosswalk/import and import your model. If you are familiar with XSI, set up the model as it should be and export through crosswalk (making sure to scale down the model by .03 before exporting, if your model is scaled to the sketchup person). If you are new to xsi or need help, here is a short tutorial on how to prepare the model.
Now, you need to scale down the model. The human in Sketchup is a lot bigger than the SWBF2 soldier, so scale down accordingly. 0.03 seems to be a good scale factor if your model is in proportion to the SketchUp man.
Freeze transforms by selecting the transform tab on the right side bar and select freeze all transforms.
Create a new null, rename it dummyroot, and move the Polymesh under dummyroot in the explorer window.
4: Use RepSharpshooter's Meshex Beta 3 to convert the model to msh and you're ready to go!
***Make sure youre faces are pointing in the correct direction before exporting (white side is what the player will see, blue they will not)***
If you're having problems with collision, create an option file with -donotmergecollision for the model, and adjust the date stamp on the .msh so it will munge. (This is recomended for every model, though not always necessary.)
If your model is gigantic or is so big you can't even see it, make sure you remembered to scale down the model and freeze transforms before exporting.
XSI doesn't like Sketchup's groups, so if parts of your model are in a group, explode them before exporting.
This is for the people who can't get XSI to work, or like the ease of making models and applying textures in SketchUp, or both, like me. I hope this helps you SketchUp users.
Thanks go to FragMe!, DarthD.U.C.K., Obiboba3po, Bobfinkl, and kinetosimpetus for helping me with the xsi portion of this when my comp wouldn't run xsi. Also thanks to RepSharpshooter for MeshEx.
I put a lot of work into figuring some of this stuff out, so please don't claim this tut as your own- Commander_Fett