If you need a refresher course for CPR, the University of Washington School of Medicine has a site with information guides and video demonstrations for CPR and choking first aid. All ages are covered, from infants to adults. There’s also an FAQ about choking and CPR.
The first (and last) adult CPR class I took was in high school, and since then the American Heart Association now teaches thirty chest compressions, instead of five. The same goes for children.
There’s a lot of good information here, but it’s obviously no substitution for licensed instruction. Visit the AHA to find a CPR class in your area.