When I first started using Expression Blend, I was a little thrown off by the zoom function when I srcrolled my mouse.
While it Is a cool feature, you may prefer to set the scroll on your mouse to...... well.......scroll. :0)
Here's how:
Go to the top menu and choose:
Edit > Options > General or Ctrl + k
When the dialog box appears selct:
"Verticl Scrolling" under the "Mose Wheel" section.
Then select: "OK"
Adn there you have it.