PowerPoint slides should support you, not vice versa. You should avoid turning toward the screen (i.e., away from your audience) to refer to slides or to point something out. Place a laptop computer on a table in front of you and use a wireless mouse to change the slides. In this way, you can always be looking forward, knowing that the slides on your laptop are the same as the slides on the screen.
If your slides are built correctly, there should be no need for pointing–it actually can be an insult to your audience. If you absolutely must point to or trace something, use the computer’s cursor rather than physically pointing at the screen (or the touchpad if you are using a “clicker” instead of a mouse). The idea is to maintain as much eye contact as possible with your audience and not “defer” to the slides, making them the center of attention. If your audience is going to watch a slide show, you don’t need to be there.
And, above all, avoid using physical pointers or laser beams. They add absolutely nothing to your presentation and can distract audiences from what you are saying. Moreover, nervous speakers tend to play with pointers, making them appear even more nervous.