Visio is also a great and fast simple vector drawing tool for instructions, if you save your pictures to EMF. Something you’ve used and demonstrated on many occasions.

A little tip with Microsoft Powerpoint
You can use the rich animation features built into PowerPoint to achieve some pretty easy effects, even motion tweens (Flash term) without Illustrator.

In most cases for training, presentations and instruction, I find animation is used mostly to move, hide and show objects based around the concept of a timeline. Since powerpoint already gives you triggers, transitions, layers and timers, you can queue a sequence of these effects to achieve some pretty powerful effects. Capture the animation in camtasia so you can export to an AVI file and you have a fast, convenient animation to include in other video only projects.

However, I think Flash is a way more efficient and versatile tool and can do much better complex animation tweens (such as repetitive moving parts of a machine or complex interactions between specific objects) all within a very small file, which is impossible with PowerPoint, of course.