Two authors you can't go wrong with would be O'Mura and Finkelstein. For a somewhat different approach you can try AutoCAD 2007 3-D Modeling by Alan J. Kalameja.
Sorry, but I cannot make any recommendations re: books on Inventor or Mechanical Desktop but I'm sure another forum member will be able to help you out.
When you assemble a portfolio of drawings make sure to do it in as professional a manner as possible. A sloppy and disorganized portfolio will put off many a prospective employer. Good luck in your job search.