Although I can't see what versions you have available to you (since that URL would only link back to my personal account) I know that with, for example, the latest version of the controls you get the .NET 2.0 assemblies included with your install. So when you have finished installing the RadControls for ASP.NET Ajax you can either find the assemblies in the Bin folder of your installation folder (usually Program Files/Telerik/RadControls for ASP.NET Ajax/ or something similar). There are two folders (or three if you have .NET 4.0 installed) which are Bin (.NET 2.0), Bin35 (.NET 3.5) and Bin40 (.NET 4.0).
Aside from this, if you use the configuration wizard that has been available in the last couple of versions of the RadControls it should automatically use the proper assemblies for whatever framework your application is building against.