one way:

Thread oThread = new Thread(new ThreadStart(delegate()
{
    do_this_and_that();
}));
oThread.Start();

threw an exception of type 'Microsoft.VisualStudio.Debugger.Runtime.CrossThreadMessagingException'

solution:

textBox1.Invoke(       new MethodInvoker(           delegate { textBox1.AppendText("."); }));

System.Windows.Forms.Application.DoEvents();