Here's what worked for me (also see above by "rushnut, on Oct 22, 2009 2:01:28 pm BST"):
From the Control Panel, select "Add or Remove Programs". On the left side of the Add/Remove Programs window click "Add or Remove Windows Components". This opens "Windows Components Wizard". Internet Explorer should be on the list. Check the box, click "Next", and the progress window should say windows is configuring the component. Once you click Finish, the Internet Explorer icon should appear on the Start Menu ("All Programs"). I launched from this icon and it definitely opened IE version 8 (even though parts of version 7 are still lurking on my computer and I can't get rid of them even after multiple uninstalls).
After you get Internet Explorer working, I highly recommend you go to Mozilla.com and download FIREFOX!!!
(and set Firefox as your default browser). I can't stand IE and all the crap it puts on my computer -- Firefox doesn't do this. And Firefox doesn't get hit by all those viruses written for IE so it's a lot safer for your computer.
I only use IE for web sites that are specifically Not compatible with Firefox!