Why can't I extract the ns-2.1b5 file with winzip?

[yuanjn@sdp.ee.tsinghua.edu.cn (Yuan Jian)]

I am looking forward to using NS to analyse,but when I downloaded it with great difficulties,I

found it could not extract with winzip7.0.I don't know why.I am very dissappointed and wait for

your advice.Thank you.   

               

                                                                One who nead your help