I'm having a friend help with mapping while I handle other parts of the map building process, and he asked me to find out how to blend textures.

make two terrain patches that can overlap perfectly, in one of them put a non-blend(it cant be made to be transparent) texture and it the top one that blends(has "_blend" prefix at the end) the selecting the top one press y, a meny will appear and select the options "alpha" and "flatten" then in 3d preview start the blending moving the mouse over the patch vertices while holding (i dont remember if it was "alt" or "shift" or "control") hehe