I have compiled the Ajax.NET library for the Microsoft .NET Framework 2.0 (beta). You can download the ajax.dll from http://ajax.schwarz-interactive.de/download/ajaxbeta.zip . If you have time please give me some feedback if it is running or not in your ASP.NET 2.0 projects.
Note: If you are using your own IAjaxObjectConverters and you have put the code for this in the App_Code folder you have to change your web.config to use the assembly "App_Code" instead of i.e. "CSharpSample".