Export to excel 2007 ASP.NET

Hi,

I trying to export the gridview data to excel 2007 it is working fine in
windows xp prompting a dialogbox save, cancel,open, when we are accesing the
url from client machine where windows vista has got installed on it, it is
not asking for open,save dialog box rather it directly asking for dialogbox
"file is of different type do you want to open it"

I want open,save ,cancel dialog box tobe prompted and it should not ask for
above message ie, 'do u want to open'


can anybody help me out its urgent