以下の情報をベースにして改造してみた。
http://outlooklab.wordpress.com/2008/04/12/%e3%83%86%e3%83%b3%e3%83%97%e3%83%ac%e3%83%bc%e3%83%88%e3%81%ab%e8%87%aa%e5%8b%95%e3%81%a7%e4%bb%8a%e6%97%a5%e3%81%ae%e6%97%a5%e4%bb%98%e3%82%92%e8%a8%ad%e5%ae%9a%e3%81%99%e3%82%8b%e3%83%9e%e3%82%af/

Public Sub OpenTemplateWithDate()
    Const TEMPLATE_FILE = "c:\temp\test.oft"
    Dim objItem As MailItem
   
    Dim dt As String
    Dim tm As String
    Dim wkdy As String
   
    dt = Format(Now, "mm/dd")
    tm = Format(Now, "hh:nn")
    wkdy = Format(dt, "AAA")
   
    Set objItem = Application.CreateItemFromTemplate(TEMPLATE_FILE)
   
    objItem.Subject = Replace(objItem.Subject, "mm/dd", dt)
    objItem.Subject = Replace(objItem.Subject, "WKDY", wkdy)
   
    objItem.Body = Replace(objItem.Body, "mm/dd", dt)
    objItem.Body = Replace(objItem.Body, "WKDY", wkdy)
    objItem.Body = Replace(objItem.Body, "hh:mm", tm)
   
    objItem.Display
End Sub