Hi there.

You must need too set textures to CLAMP mode and enable 2 texture stages for 2 different textures.
Then you must just set UV for every vertex like this (clockwise from top):
1st texture:
0.5 0.0
1.5 1.0
0.5 1.0

2nd texture:
-0.5 0
0.5 1.0
-0.5 1.0

Something like that. Or you can try different way by deviding your triangle with 3. And put first texture into 2 triangles and a second ine on third triangle.