How to determine which SQL Server user or database overuses server resources
There's a ton of dynamic management views (DMVs) you can use to get the data, but the easiest way is to use Adam Machanic's sp_WhoIsActive stored proc.  Here's a video on how to use it:

http://www.brentozar.com/archive/2010/09/sql-server-dba-scripts-how-to-find-slow-sql-server-queries/

And you can download it from here:

http://whoisactive.com/

The output includes columns for the database name, CPU cycles used, query duration, and more.