The words personal and personnel are related, but not identical, in meaning. And they're pronounced differently.

The adjective personal (with the stress on the first syllable) means "private" or "individual."

The noun personnel (stress on the last syllable) refers to the people employed in an organization, business, or service.

See the usage notes below. Also see: personal essay.

Examples:

• "The summer stretched golden in front of us with promises of picnics and fish frys, blackberry hunts and croquet games till dark. It would have taken a personal loss to penetrate my sense of well-being."
  (Maya Angelou, I Know Why the Caged Bird Sings. Random House, 1969)

• "The true teacher defends his pupils against his own personal influence. He inspires self-trust. He guides their eyes from himself to the spirit that quickens him."
  (A. Bronson Alcott)
• "Outstanding leaders go out of their way to boost the self-esteem of their personnel."
  (Sam Walton)

Usage Notes:

• "A surprisingly large number of books warn against confusing these two words. Such confusion would appear unlikely because they are pronounced differently and function as different parts of speech. It is possible that they both may be misspelled sometimes as personel."
  (Merriam-Webster's Concise Dictionary of English Usage, 2002)
• "Personal is often criticized as being redundant: That’s my personal opinion is wordier but not otherwise different from That’s my opinion. But some other applications of this very high frequency word seem to impart useful information: She has an entourage of some size, including her personal maid, her personal secretary, and her personal trainer. We understand these people to be dedicated, like personal computers, to the requirements of this one woman; the idea of exclusivity adds to our sense of her importance, even if the use of personal doesn’t add much other information.
  
  "Personal and personnel come from the same root, but they are spelled and pronounced differently (PUHR-suhn-uhl and PUHR-suhn-NEL) and have only person in common: personnel as noun means 'people, especially employees,' and 'the field of employee matters itself' and as adjective refers to 'departments responsible for hiring and keeping records about the employees of an enterprise.'"
  (Kenneth G. Wilson, The Columbia Guide to Standard American English, Columbia University Press, 1993)

Practice:

(a) "Most people in big companies are administered, not led. They are treated as _____, not people."
(Robert Townsend)

(b) "Amelia believed she had a _____ mission to intercede on behalf of any horse she saw being mistreated."
(Susan Butler, East to the Dawn: The Life of Amelia Earhart. Da Capo, 1999)

Answers to Practice Exercises

Glossary of Usage: Index of Commonly Confused Words