Something

using Irc;
using Irc.Net;
using System.Windows.Forms;

[assembly: Plugin(typeof(TestPlugin.Test))]
namespace TestPlugin
{
	public class Test : Plugin
	{
		private Main mainForm;
		public bool Initialize(Main mainForm)
		{
			this.mainForm = mainForm;
			foreach(Client c in mainForm.GetConnectedNetworks())
			{
				c.PublicMessageEventHandler += MessageResponder;
			}
			return true;
		}
		public void Dispose()
		{
			foreach(Client c in mainForm.GetConnectedNetworks())
			{
				c.PublicMessageEventHandler -= MessageResponder;
			}
		}
		private void MessageResponder(object sender, MessageEventArgs e)
		{
			if(e.Message == "who are you?")
				((Client)sender).Say(e.Channel.Name, "I am an IRC.NET plugin. Nice to meet you!");
		}
	}
}