My [very strong] advice is not to do a live demo DURING YOUR POWERPOINT PITCH. You'll absolutely need to do a demo at a later point (perhaps even immediately following your pitch presentation), but what we're talking about here is a very specific piece of performance art: a carefully-tuned, 15-20 minute presentation which is usually presented in front of a group (either a formal group of angels, or a smaller group of VCs). For this presentation, you want as much control as possible, where NOTHING can go wrong.

You can deliver 200% of the value of a live demo in a CANNED demo (or screen shots of a demo). There is no time spent moving between screens, no chance that a bad connection or temporary glitch will make you look like an idiot, no chance that Murphy's Law will rear its ugly head.

Think of this as one of the [very important] communications pieces in your arsenal. You'll also need an elevator pitch (60 seconds, max, no slides), a business plan (so you know what your business is all about), an executive summary (which is what the investor usually reads), handouts to leave behind after your presentation (these are NOT your slides!), and, increasingly these days, a short (5 minute) video, which can be uploaded to the angel's or investor's web site if you're asked to submit your materials that way.