In the LINQ preview (CTP May 2006), the Smart Tags functionality in the C# IDE does not work correctly. In particular, I miss the "Resolve" feature that puts in the necessary "using" statements automatically. But the good news is that it is easy to get this functionality back:

1. Start up RegEdit.exe
 

2. Open HKEY_LOCAL_MACHINE\Software\Microsoft\VisualStudio\8.0\Packages\{A066E284-DCAB-11D2-B551-00C04F68D4DB}\SatelliteDLL

3. Edit the "Path" value and change it from "C:\Program Files\Microsoft Visual Studio 8\VC#\VCSPackages\1033\" to "C:\Program Files\Microsoft Visual Studio 8\VC#\VCSPackages\"

4. Then open a console window, go to the directory where your Visual Studio devenv.exe is located (e.g. C:\Program Files\Microsoft Visual Studio 8\Common7\IDE) and run
   devenv /setup /resetuserdata /resetsettings
(be patient, this takes a while).

See http://forums.microsoft.com/MSDN/ShowPost.aspx?PostID=419975&SiteID=1