problem of Multitexture

I want to apply two textures to a single fragment,but I don’t want to use the API glMultiTexCoord2f because I want to make it without the help of hardware. Then what should I do?
I have ever noticed that someone said in his blog that mutiple rendering can help me,but I don’t know what’s that mean.
I’m a beginners of opengl,so the answer of you is the more detailed the better.
thank you.

Do not cross-post.