Consuming a geoprocessing custom model in .NET
Module1.vb
' Copyright 2012 ESRI
' 
' All rights reserved under the copyright laws of the United States
' and applicable international laws, treaties, and conventions.
' 
' You may freely redistribute and use this sample code, with or
' without modification, provided you include the original copyright
' notice and use restrictions.
' 
' See the use restrictions.
' 

Imports ESRI.ArcGIS.esriSystem
Imports ESRI.ArcGIS.Geoprocessing

Module Module1

    Private m_AOLicenseInitializer As LicenseInitializer = New GeoprocessingInDotNet2008.LicenseInitializer()
    <STAThread()> _
    Sub Main()

        ' Load the product code and version to the version manager
        ESRI.ArcGIS.RuntimeManager.Bind(ESRI.ArcGIS.ProductCode.Desktop)

        'ESRI License Initializer generated code.
        m_AOLicenseInitializer.InitializeApplication(New esriLicenseProductCode() {esriLicenseProductCode.esriLicenseProductCodeAdvanced}, _
        New esriLicenseExtensionCode() {})

        ' Create geoprocessor. Overwrite true will replace existing output
        Dim gp As IGeoProcessor2 = New GeoProcessor()
        gp.OverwriteOutput = True

        ' Get the workspace from the user
        Console.WriteLine("Enter the path to folder where you copied the data folder.")
        Console.WriteLine("Example: C:\AirportsAndGolf\data")
        Console.Write(">")
        Dim wks As String = Console.ReadLine()

        ' Set the workspace to the value user entered
        gp.SetEnvironmentValue("workspace", wks + "\golf.gdb")

        ' Add the custom toolbox to geoprocessor
        gp.AddToolbox(wks + "\Find Golf Courses.tbx")

        ' Create a variant - data are in the workspace
        Dim parameters As IVariantArray = New VarArray()
        parameters.Add("Airports")
        parameters.Add("8 Miles")
        parameters.Add("Golf")
        parameters.Add("GolfNearAirports")

        Dim sev As Object = Nothing

        Try
            gp.Execute("GolfFinder", parameters, Nothing)
            Console.WriteLine(gp.GetMessages(sev))
        Catch ex As Exception
            Console.WriteLine(ex.Message)
            Dim errorMsgs As String = gp.GetMessages(sev)
            Console.WriteLine(errorMsgs)
        Finally
            Console.WriteLine("Hit Enter to quit")
            Console.ReadLine()    ' pause the console to see messages
        End Try

        'ESRI License Initializer generated code.
        'Do not make any call to ArcObjects after ShutDownApplication()
        m_AOLicenseInitializer.ShutdownApplication()
    End Sub

End Module