都很适合学习，有时间再翻译
Use ASP.NET with AJAX to make your chat application; there are many good article and examples:
Building an AJAX based chat room in ASP.NET
http://www.codeproject.com/KB/ajax/UChat.aspx
Simple chat application for ASP.NET
http://www.codeproject.com/KB/applications/SimpleChat.aspx
Build a Web Chat Application using ASP.Net 3.5, LINQ and AJAX (in C# 3.5 or VB 9.0)
http://www.codeproject.com/KB/aspnet/WebChatAsp35LinqAjax.aspx
Multi User Chat Room Using ASP.NET 2.0 and AJAX
http://www.codeproject.com/KB/aspnet/ASPNetChat.aspx