The status of the latest Reporting Services beta is explained here by Brian Welker from Microsoft:
The Report Designer Preview is an early build of the next version of Report Builder. While all the features are not finished yet, it should give you a good idea about the direction of the product
If you are using the current CTP, you will notice that Report Designer is unchanged from RS 2005 and still hosted in the VS 2005 shell. We are in the midst of integrating the RS 2008 layout surface into the VS 2008 shell and expect this to be available in the next CTP.