You can use multiple textures in FPSC.. it's a tricky thing to figure out. I'm going to be posting a video tutorial showing how to do it in a while here.
essentially you need an .fx shader applied to the model, and you can apply it to the FPE...
here's an example the legendary COZ created for my latest model..
(THE BELOW ENTERED IS THE FPE SCRIPT>> NOT THIS STUFF)
;visualinfo
effect = effectbankCoZshader1.fx
textured = Diffuse Color_D.tga
texturen = Diffuse Color_N.dds
textures = Diffuse Color_S.dds
castshadow = 0
(BELOW IS NOT SCRIPT STUFF.. I HAVE TO SPECIFY THAT OR IT IS EASY TO GET LOST)
So, basically.. you open the .FPE and you will find the "Textured" slot, but not the other two.. you have to enter them in manually.. as well as the "effect" slot.. its as easy as copy and paste... and don't mind the".dds" extension, you can also use ".tga" for images.. AND MAKE SURE THE TEXTURES ARE IN THE SAME FOLDER AS THE ENTITY!!
now.. as for MAX and the render to texture problem.. I'm not sure why it would come out Jagged, but you may want to "Reset XForm".. that may likely help.. but I dunno for sure.
If you have any modeling questions you can check out my youtube page.. though I specialize more in high polygon modeling, but it lends itself well to this sort of stuff... I'm going to be making some tutorials on FPSC modeling stuff pretty soon here.
http://www.youtube.com/user/Screenwriter805