dreamweaver courses - Navigation

Hello all

I have very recently started to use Dreamweaver 2004 mx and although a superb program i have run into a problem allready..when i create a left navigation bar it moves up and down when i view it when clicking on another link in the same nav table,(i think its to do with percent or pixels?)..and when i add images to the index and other pages it moves up and down then also when the different links are clicked..im sorry to ask such a newbie question but it is becoming frustrating for me and i cant seem to keep the nav bar in one place when images and text are inserted.Can anyone shed some light on this for me please?

Many thnx

Simon B