You can download SQL Server 2008 Native Client here:  http://www.microsoft.com/downloads/details.aspx?FamilyId=C6C3E9EF-BA29-4A43-8D69-A2BED18FE73C&displaylang=en

You can download SQL Server 2005 Native Client from here: http://www.microsoft.com/downloads/details.aspx?FamilyID=536fd7d5-013f-49bc-9fc7-77dede4bb075&displaylang=en