"I have an import specification and everything works fine. What I need to check before the import commences is that he has selected the correct file with the correct column count, as there are two possible imports"

You could open the file and inspect the first line. If the number of " (double quotes) does not agree with your spec, then you alert the user and halt the import:

Function CountQuotes()
	Dim s As String, x As Long, y As Long
	Open "mytextfile" For Input As #1
	Line Input #1, s
	Close #1
	For x =1 to len(s)
	    If mid(s,x,1) = Chr(34) Then y=y+1
	Next x
	' at this point, s holds the full text of the first line of the file
	' y = number of " marks in the text of s
	CountQuotes = y
End Function