I spent an entire summer doing almost nothing but searching job sites/newspaper classifieds, submitting resumes and just trying like hell every day. I had about three or four interviews that resulted in rejections. Four months in, I got my fast-food job.
This was last year. Sadly, the economy has gotten worse since then. I would say that half (or even more than half) of your difficulties in finding a job may be due to that. I know a lot of people who are *normal*

and they've been unemployed for months.
What I did is pretty much all you can do--just keep trying, relentlessly. Finding a job will have to become your job. Yes, it does s**k. However, it will probably pay off, perhaps sooner than you think.
How to get through the interview: it's one giant act/performance. You are, quite literally, being someone else--the right person for the particular job you're seeking. Research the job beforehand so you know exactly who/what they are looking for and can answer questions properly. Bring your resume and a notebook and pen to the interview. Most interviewers take notice of someone who appears prepared and interested.
General tips: only answer the questions they ask--don't add anything unless they request it. Be aware of what your body is doing and force it to "behave." Fold your hands in your lap, keep your feet still--whatever is needed. When speaking, try to keep your tone constant--not a "monotone," but "calm." Same with the pacing of your speech. Practice beforehand with a friend if it helps.
No, this isn't easy. It was incredibly difficult at first. Just like anything else, it takes practice.
I hope that helps somewhat. Above all else, try not to get discouraged. Like I said, the economy is largely to blame.
Good luck.
