You access an IBuildServer object by calling the SearchAdmin.BuildServer property, as in the following example, where objBuildServer is the name you give to the IBuildServer object:
Option Explicit
On Error Resume Next
Dim objSearchAdmin, objBuildServer
Set objSearchAdmin = CreateObject("Search.SearchAdmin.1")
Set objBuildServer = objSearchAdmin.BuildServer
...
'Release objects
Set objBuildServer = Nothing
Set objSearchAdmin = Nothing