Hi,
You can check the web.config of the webapplication on the sharepoint server. It would have entries for ajaxcontroltoolkit assembly. Also, you can check the version of AjaxControlToolkit assembly in GAC.
http://weblogs.asp.net/jan/archive/2007/02/26/using-the-ajax-control-toolkit-in-sharepoint.aspxI hope it helps.
Cheers ...
Rajendra Shekhawat