I recently picked up a Microsoft Natural Ergonomic Keyboard 4000 since I prefer to have a wired keyboard, but wanted to try out an ergonomic keyboard for a while.  I've only been using it for a day, but overall I'm quite pleased with it.  The only thing I found fairly useless was the Zoom button in the middle of the keyboard.  I very rarely zoom anything, especially a webpage.  What I do frequently do though, is scroll. Using the IntelliType software you can change the functionality of all the extra keys, but you can't modify the Zoom button behavior.

Zoom Button

Luckily you can edit commands.xml (\Program Files\Microsoft IntelliType Pro\commands.xml) and change the action performed by the Zoom button.  Open up commands.xml with a text editor and replace the following lines:

<C319 Type="6" Activator="ZoomOut" />
<C320 Type="6" Activator="ZoomIn" />

With:

<C319 Type="6" Activator="ScrollUp" />
<C320 Type="6" Activator="ScrollDown" />

I replaced it for the following applications:

<Application UniqueName="IEFrame" AppName="Internet Explorer">
<Application UniqueName="IEFrame7" AppName="Internet Explorer 7.0">
<Application UniqueName="MozillaUIWindowClass" AppName="Mozilla Firefox 1.5">

Once the changes have been made you need to reload the keyboard driver.  From the Start menu choose Run and type mskey and press enter.  Microsoft Keyboard Diagnostics should load.  From the Actions menu choose Close IntelliType Pro.  Then re-launch IntelliType (Start, Run, "C:\Program Files\Microsoft IntelliType Pro\DPLaunch.exe" keyboard cpl) or by choosing Microsoft Keyboard from the Microsoft Keyboard Start Menu group.  Adjusting the Zooming speed in IntelliType will also control the Scrolling speed.