Rod,
One thing I would always make sure of is that in the top of your CSS file you zero EVERYTHING out. I add this little piece of code to every CSS document I have:
Code:
ul,ol,li,h1,h2,h3,h4,h5,h6,pre,form,body,html,p,blockquote,fieldset,input,label,div,dd,dt,dl,table,tr,td { margin:0; padding:0; }
This code makes sure that no matter what browser your using the margins and paddings will start at 0 so that you can set everything yourself.
Also when your using floats make sure that you clear them out at the bottom of the last float. This can cause a lot of headaches if you don't know to clear them.