Forum Moderators: not2easy
The fix--and sorry, but without code it's impossible to be more specific than to say 'read this stuff'--is to ensure that both browsers render the page in standards mode instead of quirks mode [google.com]. Usually this can be achieved just by adding a complete doctype [google.com] to your documents as jessejump has already suggested, but there may be other factors at work causing IE to render in quirks mode even if a proper doctype is present.
Start by running your pages through the html [validator.w3.org] and css [jigsaw.w3.org] validators and correcting the problems they flag.
-b