Try this :
1. In IE7 click on Tools, Internet Options and then the Programs tab.
Click the button Make Default.
Also put a check in the box marked "Tell me if IE is not the Default browser"

2. In IE7 click on Tools, Internet Options and the Advanced tab.
At the bottom where it says "Reset Internet Explorer Settings" click the Reset button.

3. Go into the Control Panel and double click on the Add/Remove Porgrams icon.
Click the button on the left "Set Programs Access and Defaults"
In the righthand pane click on Custom and click the blue arrowheads to expand everything.
Choose Internet Explorer as your Default Web Browser.
Choose Outlook Express as your default e-mail Program.
Click OK.