Just erase all the entries (except Standard) from the registry: HKEY_CURRENT_USER\Software\Microsoft\Internet Explorer\TabbedBrowsing\NewTabPage\Exclude
With IE9 (Beta) comes a new feature in the about:tabs page wich displays favourite websites. You can increase the number of sites with a simple registry hack:
Open RegEdit and create a new DWORD value called NumRows and give it a value between 2 and 5 in HKEY_CURRENT_USER\Software\Microsoft\Internet Explorer\TabbedBrowsing\NewTabPage
Hopefully this will be easier with the non-beta release..