One of my Quality Control Person gave me list of Bugs related to the contorls on IE8 though everything else works fine on IE7/IE6/Firefox and the site was build under Microsoft .net 2005.For an instance the asp.net menu do not work on IE8 beta, is it an IE8 bug or shall we avoid IE8 Beta for testing unltill Microsoft launches full IE8.

I wouldn't worry about testing for IE8 until well after it is released.  Based on reports I've seen IE8 may have significant issues with rendering common pages, which will likely prevent it from being adopted as fast as IE7 was.