FileDateTime Function:

The FileDateTime function returns the time and date a file was last modified. If the file is not found or an error occurs during the processing of the function, Null is returned.

datetime = FileDateTime(pathname)
Example Usage:
<% = FileDateTime( server.mappath("/New Folder/file.asp") ) %>
ASP Source Code:
Private Function FileDateTime(byVal pathname)
	Dim objFSO, objFile
	On Error Resume Next
	Set objFSO	= Server.CreateObject("Scripting.FileSystemObject")
	Set objFile	= objFSO.GetFile(pathname)
	If Err Then
		FileDateTime	= Null
		FileDateTime	= CDate( objFile.DateLastModified )
	End If
	Set objFile	= Nothing
	Set objFSO	= Nothing
	On Error GoTo 0
End Function