Visual Studios 2008 has a new feature called Multi-targeting. This feature enables you to have the ability to control which version of the .net framework to use in your project. It allows you to use multiple versions of the framework from within the same environment.
When you choose a particular framework the IDE will be automatically change the surroundings (controls, dialog boxs, even intellisense etc.) to accomodate the chosen framework.
Check out Amanda Silvers blog entry about VS 2008 Beta 1 Codenamed Orcas features including multi-targeting for more information.
Hope that helps.