Thanks guys, after trying texture transformations, pixel shaders, polygon subdivision... Finally I found that the only acceptable way to tile a part of a texture in a primitive is exactly what juhaszt suggested. To subdivide the primitive into a list of triangles, giving each triangle in the list its proper part of the texture.

I found that it''s also possible to use a pixel shader, and Tride even wrote an example for me (thanks Tride, http://www-imagis.imag.fr/Membres/Sylvain.Lefebvre/repeat). But since it needs very new hardware work, it''s an unacceptable solution.

Also, texture transformations will definetily not work with this, since texture transformations are done before coordinate wrapping.

Thanks for your help.