Could someone please help me, what is the difference between a normal sound card and a "full dulpex" sound card? I'm trying to look intellegent to my son, but I don't know.

Hi Steve!
Although 'duplex' or 'full duplex' is a general term:
http://coverage.cnet.com/Resources/Info/Glossary/Terms/duplex.html
for 'full duplex' soundcard owners, it means that you can play and record at the same time: essential if you want to use your PC as an Internet phone, e.g. Most modern cards are full-duplex I would think...