1) I'd question the need for two elements there, the extra outer div might be unnecessary.
2) border is added TO width, so if you declare the same width on both, and put two px padding, you've got a 924px wide ul inside a 920px content area on the outer div.
This is why as a rule I have a single outer div to set the width for everything, then let all the child elements do the normal block behavior of filling whatever's available.
Much less what on earth are you APo'ing the child UL for?!?
You've over-thought... everything; for meaningful help though, we'd have to see the actual page it's on; but that extra DIV for nothing and APo of the UL is throwing up alarms here.