I'll be honest; PowerPoint is one of those applications that I treat rather harshly. I've been put off by too many awful presentations with whooshing bullet points, dreadful clip art and perhaps even a few sound effects for good measure. As far as I'm concerned, PowerPoint is a tool for creating nightmares. Horrible, bullet point riddled nightmares.
User Interface design is something of a dark art, and can be particularly difficult for programmers. Mocking up a few screens in paint is handy, but stringing them together and adding the correct hotspots can really help you visualise how it's all going to work. It's quite easy to put together a few slides with fake buttons, and I managed to get a rough prototype up and running within a few hours. Not bad for someone with “limited” art skills and a general distrust of all things PowerPoint. I was pleasantly surprised by how easy it all was, and just seeing it working gave me plenty of ideas for improvements.
One of the most enlightening things you can ever see is someone trying to use the interface you've designed. Having an interactive prototype makes it much easier to see how they react to the choices in front of them. Even if you can't get to watch someone use your interface, sending your presentation to a few people to try out can still generate valuable feedback.
I highly recommend giving Jensen Harris's blog a read. It's a fascinating insight into how a large company like Microsoft designs and tests user interfaces, and shows off some of the new features of Office 12.
Read more: Jensen Harris: An Office User Interface Blog