Have you installed IE8?
What anti-virus application or security suite is installed, is your
subscription current, and is it supported in IE8? What anti-spyware
applications (other than Defender)? What third-party firewall (if any)?
Were any of these applications running in the background when you installed
IE8?
Has a Norton or McAfee application ever been installed on this machine
(e.g., a free-trial version that came preinstalled when you bought it)?
Is "Cumulative Security Update for Internet Explorer 7 for Vista (KB969897)"
listed in Installed Updates?
Just asking for now!! Do NOT use such a Restore Point yet!! => Do you have
an available Restore Point which predates the install of IE8?
NB: Uninstalling IE8 (cf.
http://support.microsoft.com/kb/957700) should
resolve the behavior but you should not have encountered it in the first
place if IE8 was installed properly.