Microsoft released recently templates for VS 2008 that you can use to create websites or applications targeting .NET 2.0 and using ASP.NET 2.0 Ajax Extensions 1.0.
Brad Adams has a post about that, check it out: http://blogs.msdn.com/brada/archive/2007/12/19/using-vs2008-to-target-net-framework-2-0-with-asp-net-ajax.aspx
Hope this helps,
Regards
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