protected override void ProcessRecord()
{
    //Make sure both -Name and -Default aren't specified
    if (!string.IsNullOrEmpty(_Name) && _Default.IsPresent)
    {
        WriteError(new ErrorRecord(
            new ArgumentException(
                "Default and Name parameters can't both be specified"),
            "DefaultAndName",
            ErrorCategory.InvalidArgument,
            null));

        return;
    }

    //If the machine name is not specified, assume the local machine 
    //(via the "." value)
    string machine = string.IsNullOrEmpty(_MachineName) ? "." : _MachineName;

    //Connect to the specified machine via the SMO WMI ManagedComputer object
    SmoWmi.ManagedComputer mc = new SmoWmi.ManagedComputer(machine);

    if (string.IsNullOrEmpty(_Name) && !_Default.IsPresent)
    {
        //If neither Name or Default are specified, write all the 
        //server instances on specified machine
        foreach (SmoWmi.ServerInstance si in mc.ServerInstances)
            WriteServerObject(si);

        return;
    }

    string instanceName = _Default.IsPresent ? "MSSQLSERVER" : _Name;

    if (mc.ServerInstances.Contains(instanceName))
        WriteServerObject(mc.ServerInstances[instanceName]);
    else
        WriteDebug("The specified SQL instance does not exist");
}

//Helper method to create a SMO Server object from a 
//SMO WMI ServerInstance object and write it to the pipeline
private void WriteServerObject(SmoWmi.ServerInstance si)
{
    if (si.Name == "MSSQLSERVER")
        WriteObject(new Smo.Server(si.Parent.Name));
    else
        WriteObject(new Smo.Server(si.Parent.Name + "\\" + si.Name));
}