An update to the silverlight tools for Visual Studio 2008 Beta 2 has been submitted to the microsoft download center. It takes a bit of time for it to propogate through the download servers, it depends on the server you hit as to which version you'll get. So wait a while until you download, and it should be there. Sorry, I don't have a way of knowing when it'll finally be there. The download page is at http://www.microsoft.com/downloads/details.aspx?FamilyID=b52aeb39-1f10-49a6-85fc-a0a19cac99af&DisplayLang=en.
Edit: Looks like its up there for me now
To know if you have the newer version, download it to disk, then right click and open the properties dialog. In the details panel, your looking for a file version of "9.0.20706.18". The key number your looking for is the final "18", if it says "12" then you have the original release.
The changes in this release are:
Please uninstall the old silverlight tools release before installing this one, to ensure you have the updates. You should not need to remove/reinstall the silverlight 1.1 alpha refresh runtime if you allready have it installed.
If you have added the registry key because of the guid change, you'll probably want to remove that.