Since others may experience the same problem or have their own reasons for removing the IE9 beta I thought info on how to remove the beta would be useful – so here you go.
Start off by opening the Control Panel and selecting Uninstall a program:
Once the Control Panel is open you will need to View installed updates by clicking on that link in the left hand column of the dialog:
Under the Microsoft Windows listing you will see an entry for Windows Internet Explorer 9 – just click on that to uninstall the IE9 Beta:
Once it is uninstalled a reboot will be required. When your system restarts IE8 will be available once again.