Scenario:  When using a VSTS 2008 or VSTS2010 database project, stored procedures and views that reference system items or items in other databases throw warnings or invalid reference errors.

Solution:  Add a database reference to your project, the hardest part, getting the .dbschema file.

Snippet:

To get the schema file, from the Command prompt

Navigate to the Deploy folder under your visual studio installation.

cd C:\Program Files (x86)\Microsoft Visual Studio 10.0\VSTSDB\Deploy

Run the following comand replacing servername and  DBName as appropriate.

vsdbcmd /a:import /cs:"Server=servername;Database=DBName;Trusted_Connection=yes; " /dsp:SQL /ModelFile:"DBName.dbschema"

Once you have the file, copy it to a location you want to reference and use the wizard in VSTS to add the database reference.  For large shops or databases that are shared across multiple projects, a dbschema library on a file share everyone could get to might be appropriate.