This step differs from the others in that Excel should not be running.
Close Excel, if it is running.
Go to the Windows Start menu and choose Run.
Enter Excel.exe /unregserver and click OK. (There is a space between ...exe and /unreg...)
When that finishes, from Windows select Start | Run again.
Run Excel.exe /regserver and click OK.
Restart your computer.
Start Excel normally and attempt to run the wizard.
If this doesn't work, more Draconian measures are needed. To see these, go to the next step.