Sounds like you need a baseline of the server and compare it after you add a new database. I would recommend you use Glenn Berry's DMV scripts to create that baseline:

http://sqlserverperformance.wordpress.com/tag/dmv-queries/

Also, if you want to create a system to capture the results check out Ted Krueger's blog post on that:

http://blogs.lessthandot.com/index.php/DataMgmt/DBAdmin/sql-server-baseline-collection

Glenn does an excellent job on giving you the metrics you need and describing what you should look for. If you have any specific questions please ask the forum.