You don't have IIS6 because IIS6 only comes with Windows 2003 so you are running IIS5 but that is not the issue. You need to remove existing SQL Server Express installed and then install the Express Advanced Toolkit edition with SP3. Check the link below and download the file to your C drive and run setup from your C drive.

http://www.microsoft.com/downloads/details.aspx?FamilyID=d434dc36-a24d-44ee-937e-553c382557e3&displaylang=en