http://www.viva64.com/en/a/0082/

VS 2005 support the then new .net framework 2.0 visual studio 2008 came out to support 3.0 and 3.5 while visual studio 2010 supports the upcoming .net framework 4.0.Also since the release of visual studio 2008 all newer versions are now backwards compatible to older frameworks. Meaning in visual studio 2008 you are able to work with .net framework 2.0 applications as well as the at the time new 3.0 and 3.5 frameworks. This means the new visual studio 2010 will support development of framework versions 2.0, 3.0, 3.5 and 4.0. Visual studio 2008 however will only support 2.0, 3.0 and 3.5.