Can I hook up a usb port to the car stereo in my ford focus?

Answer 1

they are not available now but are working on them maybe a year before we see the interface
but you can use one of this now

http://www.oemautosound.com/c-86-ford-auxiliary-input-converter.aspx

Answer 2

Universal Serial Buss is a computer digital inupt or out put device. Radio ampflication uses Analoge imputs. The optional CD player converts the digital to analong before that signal is sent to the radio. Best you can hope for is an Ipod interface or replacement radio with audio imput jacks factory installed