Like i mentioned, you can just flip the texture coordinates:
Code:
  glBegin(GL_QUADS);
    glTexCoord2f(0,1);  glVertex3f(0, 0, 0);
    glTexCoord2f(1,1);  glVertex3f(1, 0, 0);
    glTexCoord2f(1,0);  glVertex3f(1, 1, 0);
    glTexCoord2f(0,0);  glVertex3f(0, 1, 0);
  glEnd;
And also, the whole thing is only good to know when doing graphics manually. Much of 3D graphics are actual models and the texture coordinates of that system work exactly as is. Textures on 3D models look exactly the same as in modelling program.