All things being equal, I'd rather hire someone that seemed nervous in an interview than someone that seemed relaxed, as the former is a good indicator that at least they are excited about the position.
That's gotta be a very noisy signal though. I'm nervous in any interview or public speaking thing whether I care much about the thing or not.
Nervousness is also often an indicator that you may not feel fully prepared. The best way I find to relieve nervousness in these situations is to be so prepared that there's really no reason at all to be nervous.