There have been a number of problems related to IE8 breaking Visual Studio 2005/2008.
Examples:
IE8 + Visual studio error
https://connect.microsoft.com/VisualStudio/feedback/ViewFeedback.aspx?FeedbackID=426428
http://dpotter.net/Technical/2009/05/upgrading-to-ie8-breaks-debugging-with-visual-studio-2005/
Are there still specific issues with Visual Studio preventing you from installing IE8?
Best Answer
I have been working on VS2005/2008 with IE8 for several months without problem now after changed the IE security zone and tabprocgrowth setting.