I think this is now-a-days a common issue for all the developers who are currently exploring both Visual Studio 2010 RC and Silverlight 4 Beta. Microsoft has removed the bits of Silverlight in the RC version of Visual Studio 2010. To work with that lots of people are now asking the same question.
Today I found a link which is written in a different version. I thought to share this thru my blog which may help the fellow developers (who are keeping a eye to my blog posts) to explore both simultaneously. Here is the original link of the post: http://sorokoletov.com/2010/02/hate-2-wait-silverlight-4-beta-2-vs-2010-rc/
Use the below link to translate it in English: http://tinyurl.com/SL4inVS2010RC-en
If you follow the steps provided in that blog post, you can install the Silverlight 4 Beta in your Visual Studio 2010 RC environment & start working on it till Microsoft releases the RC version of Silverlight. Go ahead and enjoy.
Remember: WCF RIA Services doesn’t work with this hack. I strongly recommend you to work with Visual Studio 2010 Beta 2 & Silverlight 4 Beta.