problems with div's for IE and Firefox

here is my issue...I am created a new web site that has a header 'graphic', then a menu 'row' (horizontal menu), then a main content area, then a footer area. Each of these 'areas' (divs) has a background image associated with them. I have been 'fairly' successful in get this all to be 'centered' in my browser by using the       margin: 0 auto; setting in my stylesheet.  Then I went on to the content...the Content I was setup as two 'columns' so I setup a table to set on top of the content 'image' and setup margin-top, margin-right, values for the 'content' div which is where the table is sitting...Then I wanted to add some 'graphics' to the right column of the table and have 'divs' setting 'on top' of those graphics...I created another table to sit inside of the right column and have this secondar table have 3 rows...each row holding a 'graphic'.  This was working in IE but when I went to view it in Firefox, Firefox was having problems with the secondary table graphic being in the right place, and the text (which was defined in a div) not appearing over the graphics...I know this is all 'text' and I don't have a website to show you and there is no way for me to 'copy/paste' a screen show of what I am seeing in Firefox...Any suggestions.