|Do you have a 'scroll' mouse (one with a wheel in the middle)? Normally, if you actually click the wheel it turns into a 4-headed arrow - meant for navigating webpages. In Control Panel, check to see what the middle mouse button is set to do.|
I suspect it's a custom setting in Outlook. Outlook 2010 has a system called 'quicksteps', where buttons could be assigned to special tasks but as far as I'm aware Outlook 2007 didn't have this function unless you've magically unlocked it ;-).
"I've always been mad, I know I've been mad, like the most of us..." Pink Floyd