I noticed Microsoft is trying to push installation of IE8 through Windows Update, for the ones not ready for this change they released "The Internet Explorer 8 Blocker Toolkit". The Internet Explorer 8 Blocker Toolkit enables IT Administrators to disable automatic delivery of Internet Explorer 8 as a high-priority update via Automatic Updates and the Windows Update and Microsoft Update sites.

• For computers running Windows XP or Windows Server 2003, the Blocker Toolkit prevents the machine from receiving Internet Explorer 8 as a high-priority update via Automatic Updates and the Express install option on the Windows Update and Microsoft Update sites; Internet Explorer 8 will be listed as an optional update with the Custom install option.
• For computers running Windows Vista or Windows Server 2008, the Blocker Toolkit prevents the machine from receiving Internet Explorer 8 as an important update via Automatic Updates on the Windows Update and Microsoft Update sites; Internet Explorer 8 will be listed as an optional update.
• The Blocker Toolkit will not prevent users from manually installing Internet Explorer 8 as a Recommended update from the Windows Update or Microsoft Update sites, from the Microsoft Download Center, or from external media.
• Organizations do not need to deploy the Blocker Toolkit in environments managed with an update management solution such as Windows Server Update Services or Systems Management Server 2003. Organizations can use those products to fully manage deployment of updates released through Windows Update and Microsoft Update, including Internet Explorer 8, within their environment.
• If you used the Blocker Toolkit to block Internet Explorer 7 from being installed as a high-priority update, you need to use the Internet Explorer 8 version of the Blocker Toolkit to block Internet Explorer 8 from being installed. There are different registry keys used to block or unblock automatic delivery of Internet Explorer 7 and Internet Explorer 8.
   

System Requirements
Windows Server 2003 Service Pack 2; Windows Server 2003 Service Pack 2 x64 Edition; Windows Server 2008; Windows Vista; Windows Vista 64-bit Editions Service Pack 1; Windows Vista Business 64-bit edition; Windows Vista Enterprise 64-bit edition; Windows Vista Home Basic 64-bit edition; Windows Vista Home Premium 64-bit edition; Windows Vista Service Pack 1; Windows Vista Ultimate 64-bit edition; Windows XP Professional x64 Edition ; Windows XP Service Pack 2; Windows XP Service Pack 3

Download & adittional information can be found here.