When installing VS 2008 you need to un-install all the VS beta products and other stuff. There is a long list of products which you need to un-install and remove from your system. You can find the complete list on Scott's blog. Now, that is a long long list of things that need to be un-installed before using the released version of VS 2008. Microsoft should build a smart installer which shows you a list of items which must be un-installed in order to run VS 2008 correctly. This way you can simply click "Yes" un-install everything and then you can install the released version of VS 2008.
I have installed VS 2008 Team Suite on my machine several times now and still it is busting when loading the Silverlight Project.