Looks good in FF, I must say
(Is there a Web Developer add-on for IE7?
Unfortunately not, why would one need to adjust anything in IE?(sarcasm)...

If you do have the FF WDTools...select outline > table cells.

You will see that your left and right columns are not being contained inside their containers and you are leaving where to place this to the browser and then this is also the reason you see differing rendering between browsers