//In the Installer class of your service, add a handler for the AfterInstall event.

[RunInstaller(true)]
public partial class ProjectInstaller : System.Configuration.Install.Installer
{
    public ProjectInstaller()
    {
        InitializeComponent();
	// ... other custom Installer code here
        this.AfterInstall += new InstallEventHandler(ServiceInstaller_AfterInstall);
    }

    void ServiceInstaller_AfterInstall(object sender, InstallEventArgs e)
    {
        ServiceController sc = new ServiceController(serviceInstaller1.ServiceName);
        sc.Start();
    }
}