One thing to remember about a laptop's onboard WiFi card is that they are meant only for short ranges.
You can add a laptop like this to your home's network, but will likely be out of range of your network's AP by the time you leave your yard.
The FCC caps 2.4GHz transmissions at 30mw...not a lot to work with. Them there is microwaves, son!
A laptop with a decent Linksys PCMCIA WiFi card - AND a pigtailed external omni antenna - will give you about a half-mile of connectivity from an ISP's WL Access Point, given an unobstructed view of the tower. This access is line-of-sight dependent.
The same setup with a directional antenna, with a lot of (expensive) gain, will give you from 2-5 miles. Sounds pretty good until you realize that you must remain perfectly still with the antenna pointed directly at the AP. If the ant turns by as much as a few MOA, well, you lose your link. Same thing happens if you are near a street and a truck drives by between the laptop and the AP. You get bumped.
All in all, a laptop that has an integrated WiFi card is a good investment. I just don't recommend using it as your main connectivity solution.
I suggest you get dialup, since it is cheaper, and then look around for other viable options, so you don't wind up paying for something you cannot use much of the time.