The short of it is, sort of. There are differences between the user-agent strings of the two if you really need to know. There’s was a lively discussion on this subject in the Internet Explorer forum last year where you can learn more: http://social.msdn.microsoft.com/Forums/en-US/iewebdevelopment/thread/7ecb58ca-1869-451b-920e-a27fed69a470. It’s also worth pointing out an old bit of documentation at http://msdn.microsoft.com/en-us/library/hh801221.aspx.
But it really boils down to feature detection, because the two browsers are meant to be interchangable.