You can definitely continue to use the RadControls when you upgrade to Visual Studio 2008. If the controls do not appear in your toolbar, you can add them manually by following these directions
. Be sure that you add the correct assembly. There are two: one for .NET 2.0 (in the bin folder) and another for .NET 3.5 (in the bin35 folder).
If you continue to have questions, please don't hesitate to ask.