You can access a specific IStartPage object by calling the IStartPages.Item property. Since IStartPages is a collection, you can access all IStartPage objects using a for each loop, as in the following example, where objStartPage is the name you give to the IStartPage object:
Option Explicit
On Error Resume Next
Dim objSearchAdmin, objBuildServer, objCatalogs, objCatalog, objStartPages, objStartPage
Set objSearchAdmin = CreateObject("Search.SearchAdmin.1")
Set objBuildServer = objSearchAdmin.BuildServer
Set objCatalogs = objBuildServer.BuildCatalogs
Set objCatalog = objCatalogs("KMSampleCatalog1")
Set objStartPages = objCatalog.objStartPages
For Each objStartPage in objStartPages
...
Next
'Release objects
Set objStartPage = Nothing
Set objStartPages = Nothing
Set objCatalog = Nothing
Set objCatalogs = Nothing
Set objBuildServer = Nothing
Set objSearchAdmin = Nothing