If I was applying for a job that I found posted on HotJobs, how would I start of my cover letter?

Answer 1

Try looking at a cover letter template. The template will give you an idea on what goes into each section.
http://jobsearch.about.com/od/coverlettersamples/a/covertemplate.htm

Answer 2

You could download a free ebook on resume cover letters at the site listed below:

http://www.effective-resume-writing.com/resume-cover-letters.html

There's also a sample located there too.