The Internet Explorer 8 Beta 2 was released at August 2008.It comes with many new functions such as InPrivate browsing function.However,there are still many problem in this beta version of this Internet Explorer.
You can downgrade your IE8 to IE7 or 6 by the following way>
For Windows XP platform,just go to add or remove program and find Internet Explorer 8 Beta then remove it.Your IE version will become your previous version that you were using before you upgrade.
For Windows Vista platform,you won't be able to find IE8 Beta at the add or remove program windows.You can go to Windows Update>View Update History>Installed Updates>find Internet Explorer 8 Beta then uninstall it.
Your IE version will become Version 7 after you uninstalled.
Note:Please update(if have) your IE after your done that(uninstall Beta) through Windows Update.Some critical updates are very important.
Hope this can help you^^