It's not the use of the package you wanna worry about, it's finding the material to present and talking for ten minutes about something - allowing a couple of minutes at the end for questions, explaining diagrams (and certainly including diagrams....) that you put up and having all your resources organised will fill up a little time.

Make sure you know exactly what you are talking about, do your research, and worry about the technical side last - provided you know how to work the package.

Your presentation should have a beginning, middle and an end, leaving time for questions as above. Make everything readable and the screen not too cluttered on each slide.

Make absolutely certain you have the presentation in at least two different formats, usually CD and USB hard drive, or a floppy disk failing that, even if you have saved it to the office network

Things that make powerpoint look more professional are:

knowing all the shortcut keys you need (b for blackout is a good one for the beginning, don't wanna wait for the projector to warm up...)

using a cordless presenter if available (and a laser pointer if not)

having a cover slide and summary

being confident and not letting Bill Gates get in between you and the point you are putting across (ie. don't let the technology get in the way of your talk)

This is from my experience as a final year student giving presentations and working for a major conference venue in the midlands