This was posted on one user's group that didn't make it to the general forum
by Dominicb:

Good afternoon GeekGoddess (just love the name...)

Unfortunately you can't tell the EXACT XL version that created a file. You
could tell roughly by using this macro in the sheet you are trying to
identify:

Sub version()
a = ActiveWorkbook.FileFormat
MsgBox a
End Sub

This will return one of four values:
16 XL 2
29 XL 3
33 XL 4
39 XL 5 / 95
-4143 XL 97 onwards.

Don't know if that helps you, but it's the closest you're going to get I'm
afraid.

HTH

DominicB