Here's a really quick AutoHotkey 2-liner which lets you zoom in-and-out by just holding down the left Windows key plus your mouse's scroll wheel:

Code:
; http://www.autohotkey.com/community/viewtopic.php?t=65184
LWin & WheelUp::SendInput #{NumpadAdd}
LWin & WheelDown::SendInput #{NumpadSub}
It's AHK... so you can change the activation actions to your own preference.

Hope this helps...