Thanks for the reply. I first tried that but it didn't work like that:
<a href="mypage.aspx" accesskey="u" target="_top">User Details</a>
So, I changed the URL of the page relative to facebook, like this:
<a href="http://apps.facebook.com/myapp/mypage.aspx" target="_top">User Details</a>
This worked !! but now my problem is that my application pages appear inside a frame. If anyone right clicks and selects open frame in a new tab, he again gets the page outside the facebook frame!! What should I do to restrict this behavior?