(via http://blogs.msdn.com/sharepoint/archive/2007/11/29/preview-into-wss-3-0-sp1-and-sharepoint-server-2007-sp1.aspx)

KB for the Sharepoint 2007 AJAX support

http://support.microsoft.com/kb/941955

http://weblogs.asp.net/jan/archive/2007/02/02/scott-guthrie-asp-net-ajax-support-in-sharepoint-2007-coming-later-this-year.aspx

Get the Sharepoint 2007 AJAX toolkit from CodePlex http://www.codeplex.com/sharepointajax

Other Sharepoint AJAX posts:

http://blogs.msdn.com/italy/archive/2009/05/16/ajax-control-toolkit-nuova-versione-disponibile.aspx

SharePoint 2007 and AJAX
Using ASP.NET for AJAX in SharePoint Sites
http://weblogs.asp.net/wkriebel/archive/2005/12/27/SharePointAJAXFeedbackSample.aspx
http://weblog.vb-tech.com/nick/archive/2006/01/03/1398.aspx
http://www.sharepointblogs.com/remcoploeg/archive/2006/01/27/4854.aspx
http://www.andrewconnell.com/blog/archive/2005/07/10/1713.aspx
http://msmvps.com/blogs/anguslogan/archive/2005/07/09/56884.aspx
http://blogs.tamtam.nl/mart/AJAXSeamenMassiveMultiplayerBattleships.aspx
http://blogs.flexnetconsult.co.uk/colinbyrne/PermaLink,guid,932884be-2276-4236-8df4-f360149b5fd1.aspx
AJAX + MOSS 2007
http://blog.thekid.me.uk/archive/2007/01/19/using-asp-net-ajax-with-sharepoint-moss-2007.aspx
http://msmvps.com/blogs/anguslogan/archive/2005/07/09/56884.aspx
Sharepoint AJAX Toolkit
http://www.capdes.com/2007/02/microsoft_office_sharepoint_se.html
http://sharepoint.microsoft.com/blogs/mike/Lists/Posts/Post.aspx?ID=3
http://weblogs.asp.net/scottgu/archive/2007/02/20/asp-net-ajax-and-sharepoint.aspx
http://blogs.msdn.com/acoat/archive/2007/02/23/sharepoint-and-asp-net-ajax.aspx
Sharepoint + AJAx on Exchange
http://www.sharepointblogs.com/remcoploeg/archive/2006/01/27/4854.aspx
Sharepoint + AJAx as a Feedback Form
(via http://blogs.officezealot.com/rbedell/archive/2005/12/28/8891.aspx )
http://weblogs.asp.net/wkriebel/archive/2005/12/27/SharePointAJAXFeedbackSample.aspx