Let's look at www.microsoft.com with IE6 and with Opera 8.5 (both current patchlevels as I write this). How well do the respective browsers zoom this page?
Both browsers support zooming via Ctrl-MouseWheel. IE6 appears to offer 5 levels of zoom. Opera offers 99 levels of zoom, from 20% to 1000%.
IE6's zoom only affects text, not graphics. Opera's zoom affects the entire page.
Here are two examples of IE6's zoom capabilities.
There's some difference; not a whole lot.
Here are six examples of Opera's zoom capabilities. You're looking at a moderately modified Opera -- ignore the funky brushed metal skin and weird icons, those are my tweaks.
Zoooooom.
Q.E.D.