This is something we talk with people about ALL the time. The US might be the only country to have this misunderstanding. We were searching around online today and came across a great post on Home Barista about frothing milk for cappuccinos.
What, you say you are not a barista? No worries! This will help you, as a coffee loving consumer, order what you really want!
Quickly, here is the big difference:
Cappuccino – a 6 or 7 oz drink with equal parts espresso, milk and velvety milk foam
Latte – ranging in size from 12 to 20 (in the US), this drink has espresso, lots of milk and a bit of velvety milk foam. Many people also add flavor to this drink.
Head on over to the link above for some great reading.