passport card works for international travel by land or sea. if you travel by air you need a passport book. here is a link to fill it out online.
http://travel.state.gov/passport/passport_1738.html
you can turn them in at most post office's. I just went through all this for a 5day trip.
fyi it takes 4-6 week's and cost about $60. you can get them faster but it cost more.