See the Using the QuickTake Camera example. Look at the directions for Connecting a USB Zip Drive to a Mac . They used still photos and also provide a movie. Read the article How to Add Screen Shots to Your Technology Handouts . In most cases, it's best to provide many different options.
Some people like to read off the screen, while others prefer printed directions.
The advantage of web-based instruction is that the developer can incorporate interactive aspects such as links to other websites, practice activities, and color. If you place the instructions on the Internet, people everywhere can benefit. See TechTV Guides for examples of web-based tutorials. Many people prefer reading from paper. They can take notes on the document and file it for later use.