Airport Extreme exists as both a base station (to broadcast the generic 802.11g signal) and an internal card (to recieve any 802.11g signal). The card fits inside the Mac in its own, specifically designated spot.
Unlike the Dell, which (Im assuming) has the Centrino Mobile Technology, the Apple laptop's wireless connection is not soldered on mobo. But, then again, Apple's card is better - Centrino uses 802.11b and Apple uses the newer and better 802.11g spec. The Airport Extreme card is a 100$ extra, but it is worth it. I have it and its an excellent wireless card.