from public class Server:
        public delegate void myForm1Delegate(string passedString);
        static myForm1Delegate myForm1Del;

...

            myForm1Del = new myForm1Delegate(myMainRef.myForm1.updateLog);

...

                    myForm1Del(String.Format("Beginning to listen on {0}:{1}", ipAddress, "11000"));

from public class Form1:

        public void updateLog(string newEntry)
        {
            logBox.Items.Add(newEntry);
        }