(source: http://aspnetcoe.wordpress.com/2007/02/06/how-to-remove-recent-projects-from-visual-studio-start-page/)
To remove the projects from the list, follow these steps:
1.Close Visual Studio if it is running.
2.Start the Registry Editor (run regedit).
3.Navigate to this registry key:
HKEY_CURRENT_USER\Software\Microsoft\VisualStudio\8.0\ProjectMRUList
4.Then delete the key that has the project you do not want to keep in the list.
Caveat: The list only lists consecutive items starting from File1. So if in the above list I deleted File6, then only projects from File1 to File5 will be displayed in the recent project list. File7 and above will not be displayed. If you like File7 and above to be displayed in this case, you will need to rename one of the keys so that they form a consecutive numbered list.
