Why? Stop and think. Firstly, you are only supporting a single web browser, and it's not the most popular. Secondly (and much more importantly) if you do this you will be interfering in the user settings - if he has zoomed in or out, it's because his monitor / eyesight combination requires a zoom. Mess with that, and you will annoy people.
You can apparently do it as part of the CSS:
http://msdn.microsoft.com/en-gb/library/ie/ms531189(v=vs.85).aspx[
^] - but in practice, I'd suspect you will annoy more people than you will please.