When you click Start – Default Programs – Set Your Default Programs, Outlook 2003 entry may be missing from the Programs list even though it is installed in the system. As a result, you may be unable to set Outlook 2003 as the default e-mail client.
To restore Microsoft Outlook 2003 to the Default Programs list in Windows Vista, use one of the following methods:
Method 1 – Repair your Outlook installation
1. Start Microsoft Outlook
2. From the Help menu, click Detect and Repair
3. Insert your Office/Outlook installation media when prompted.
If the above does not work, you might want to use the tool discussed in Method 2 below.
Method 2 – Run the OL2003fix tool
Download the file OL2003Fix. Unzip and extract the contents to a folder. Double-click the file OL2003fix.exe. This tool should repair Outlook 2003 registration in the system.