Excel and word fils are not opeing with IE8 while uploding in KM folders

hi friends,

i have an issues like....

i have uploeded txt, pdf ,MS excel and word files in a km folder .

while opening the files with IE8 browser txt,pdf are opeing fine but Ms excel and word files are not opening properly, some pop up coming and asking basic authentications .

But Its working fine while using with IE7.

Please help me.

Regards,

prasad.