There are 2 potential issues that I see:
1 - IE has had trouble with position:fixed in the past. If you are using IE7+ with a valid doctype or a non-IE browser this isn't part of the problem
2 - You need to specify a width for the footer if you want the footer object to be centered. Otherwise it defaults to the full width of the page and the auto margin for the left and right get set to 0. If you want the footer bar to take up the width (like the StackOverflow notice bar) and center the text, then you need to add "text-align: center" to your definition.