Open Internet Explorer, click the Tools menu, select Internet Options. Click Programs tab and select your email client from the drop-down list. Once selected, click OK/Apply button.
Typically how its done in Xp.
I would have to agree with you WR2, the likely hood of somebody using express with win7 is low, was a quick response and I just overlooked the norm. I know express can be run in win 7, but its not often somebody does.