The problem is that you are defining the width for the anchor whic is not allowed because it is an inline element. However as you are working in quirks mode then ie allows this.
The correct answer would be to float the anchors so that they can take width and still stay on the same line.
If you are going to stay in quirks mode then an easy fix would be to use display:table-cell which gecko (mozilla etc) browsers will understand and IE will continue to use the method its using already.
Hope that helps.