Difference in diagnosing an anxiety disorders & depression disorders.

I have been reading allot lately about the revisions to the DSM-IV, and the way that these anxiety and depression disorders are diagnosed have me a bit worried. In a nutshell, from what I understand, people have to meet a certain number of criteria out of a set number of criteria to be diagnosed. The problem lies in that it seems you can mix and match criteria anyway as long as they meet the number requirement. It just seems like a really broken system to me. I may have that wrong and if I do please correct me, I'm still and undergrad. If there are any Personality Profs out there, how does one truly distinguish where the anxiety ends and the depression begins or vice versa?