As Avon says, you can only apply textures on a per surface basis, not per triangle AFAIK.
Yup, I know that, but I want per triangle... and like you and Avon said, it's certainly possible. And here's how:
http://www.blitzbasic.co.nz/codearcs/codearcs.php?code=433
I should have checked the archives more throughly in the first time... what ever you want to do, it's probably there :)