hello, new to mac... next to my clock, and speaker icon at top right of screen, there is a icon for airport? what is it and do i need it off or on? does it have anything to do with internet? just this imac on now, but am thinking of adding a pc with xp soon...im using verizon dsl for internet. someone told me if i had that airport on, i wouldnt need a router? i dont know about that. thanks