How to install an Excel Add-in (XLA or XLL) with Automation

http://support.microsoft.com/default.aspx?scid=kb;en-us;280290
Dim oXL As Object, oAddin As Object
Set oXL = CreateObject("Excel.Application")
 oXL.Workbooks.Add
Set oAddin = oXL.AddIns.Add("C:\test.xla", True)
oAddin.Installed = True
oXL.Quit
Set oXL = Nothing