[exdiogene]

Firstly uninstall the program through the Control Panel.

Then go into My Computer->C:/Program files and delete the folder called "Internet explorer" if it exists.

Next go to My Computer and click on "Tools" at the top.
Then click "folder options" then the "view" tab.
Uncheck "Hide System Folders" and click on the "Show hidden Files and Folders" raido butten. Click apply.

You should now go to (for vista but XP is similar) "c:\users\Administrator\AppData\Roaming\Micros oft" and replace Administrator with your username. Delete the "Internet Explorer" folder.

Now try to install IE8. However Firefox is much better ;)