I am new to these texturing things.... I can make cartoon style textures

But I want to start making REALISTIC textures

Can anyone help me?
I use GIMP

Well, Gimp is a nice open-source freeware. It's the same one that I use, aswell.

Anyway, if you want to become a REALISTIC artist, you must start studying.
How? Well, you can search on different art forums in the web.

This one is an awesome guide, btw:


Awesome guide :3