You access an ISitePaths object by calling the ISiteRestriction.Paths property, as in the following example, where objPaths is the name you give to the ISitePaths object:
Option Explicit
On Error Resume Next
Dim objSearchAdmin, objBuildServer, objCatalogs, objCatalog, objSites, objSite, objPaths
Set objSearchAdmin = CreateObject("Search.SearchAdmin.1")
Set objBuildServer = objSearchAdmin.BuildServer
Set objCatalogs = objBuildServer.BuildCatalogs
Set objCatalog = objCatalogs("KMSampleCatalog1")
Set objSites = objCatalog.objSites
Set objSite = objSites.Item("Microsoft.com")
Set objPaths = objSite.objPaths
...
'Release objects
Set objPaths = Nothing
Set objSite = Nothing
Set objSites = Nothing
Set objCatalog = Nothing
Set objCatalogs = Nothing
Set objBuildServer = Nothing
Set objSearchAdmin = Nothing