restrictions on filetype when browsing in asp:fileupload

I have to restrict the filetypes when we click browse in fileupload.

I want to see only xls,doc,ppt file only.

i am aware if PostedFile.ContentType, but the thing is i want to see only few filetypes when browse is clicked.

 I am also not sure if this is possible.

 Can anyone help.

Thanks in advance.

Sandy
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