I guess the best way to explain it would be like this. Say my video card only supports up to 2 texture units for multitexturing(exageration for simplicity), now say that my model had 4 texture layers. All 4 textures need to be combined together to make some sort of cool looking texture, but since it seems that glTexEnvf only works with the current texture units 1 and 2, I need to call glDrawElements again for the second two texture units. Only problem is, is that it doesn't work. What happens is that the second call to glDrawElements overwrites the previous two textures draw.
Am I suppose to use a glBlendFunc in this situation?
I want to deal with texture layers like this so that my algorithm won't even stutter if it detects differant max multitexture unit amounts.