Ok, heres a quick and hopefully comprehensive tutorial on the matter:
1)Fire up sketchup and set your modeling units to metric:centimeters.
100 cm equals 1 segment width on export to 3ds so you have a proper scale for your models.
2)Model your stuff, texture it with your textures(no colours but image textures!) All transformations done on the texture will be saved as uv information on export so you can (to a certain extent) skin them here.
3)export to 3ds (you need SU pro for that), model units must be 1:1
4)import the model in your favourite .x-export-capable model pack (milkshape can export x files and if you wish to refine your texturing it has some uv tools too, i guess)
5)make it an entity or a segment using entity workshop or the segment editor.
6)test it in FPSCreator.
Some hints:
-No blue faces in sketchup: Blue (default color) face means it is inside out and hence not visible in FPSC.
-Smoothing (STRG+Eraser on hard edges) is sometimes exported, sometimes not. Use the slider for smoothing angle instead.
-Set your model to axis origin (world center) with at least one outer edge or better the middle point of its base (can't describe better)for easier alignment afterwards.
For good tutorials and stuff on SU visit sketchucation.com and i strongly recommend SketchUp for Dummies since it gives you a Headstart on speed and efficiency- can't wait till the big Sketchup book is out, though...
I am Jacks complete lack of surprise.