If you receive the following error on a front-end web server of a WSS 3.0 farm while performing a search against Search Server 2008

Object reference not set to an instance of an object.   at Microsoft.Office.Server.Search.WebControls.CoreResultsWebPart.OnLoad(EventArgs e)
   at System.Web.UI.Control.LoadRecursive()
   at System.Web.UI.Control.LoadRecursive()
   at System.Web.UI.Control.LoadRecursive()
   at System.Web.UI.Control.LoadRecursive()
   at System.Web.UI.Control.LoadRecursive()
   at System.Web.UI.Control.LoadRecursive()
   at System.Web.UI.Control.LoadRecursive()
   at System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint)

First make sure you have the front-end web server component of Search Server 2008 installed on the server where you are performing the search.  Next, add the URL you are using to access the server in your alternate access mappings.  Within Central Administration, navigate to Operations -> Global Configuration -> Alternate Access Mappings.  "Select Add Internal URLs".  Select your web application in the Alternate Access Mapping Collection drop down list.  Specify the path and port you use to access the application (example:  http://machinename01:80).  Click Save.  There is no need for an IIS reset.  The change should immediately take effect .