Tool for identifying stored procs with deprecated syntax?
Run Upgrade advisor or you can run server side trace to Identify deprecated SQL Server code -By Aaron Bertrand.

It will show you - what will break when you upgrade to new version of sql server and change the compatibility mode to the upgraded version.

Also, when upgrading from SQL Server 2000 to 2012, consider using both the older 2008 R2 Upgrade Advisor and the new SQL 2012 Upgrade Advisor, as this will provide a more complete picture of issues you may need to fix.