smallzoo, I presume you're referring to the built-in zoom feature in IE7? (as dancave mentioned)

Whilst rather handy, this feature is still way behind the likes of Opera's zoom facility, and you can never guarantee that IE7 will handle your layout correctly when zooming.

A javascript alternative might be more reliable, but I can only guess that'll be pretty hard to code (especially if you want to get the same effect as IE7's native zoom).