is there anyway to change the texture of a sertain area of an object without having to seperate it from the whole object and the put it back?

if you are refering to having multiple material on a single mesh here is starting point with a nice video tutorial http://www.blendernation.com/2006/07/10/video-tutorial-multiple-materials-on-a-single-mesh/

you need divx codecs to view it http://www.xvidmovies.com/codec/

look up UV mapping
This page has a very good UV mapping video tut(among other good tuts)