The best way to do this is to extend the range of the access point. There are two ways to do this: passive and active. You can add a passive antenna to the WAP but the better solution is WDS. With compatible equipment you can add a second WAP and double your range.
Regarding the Issue of WiFi PC cards and external antenna ports. Very few do because of FCC certification of their built-in antenna. I’ve been pursuing this issue for more than two years, because even my hand(s) on the keyboard actually attenuate (reduce) the signal strength the PC Card gets. Yes, the Lucent-Orinoco/(now) Proxim cards have a port as do SMC cards. However, D-Link, LinkSys and others at trade shows refuse to address the issue of external antenna connectors.
The problem for vendors is that they get FCC certification without external connectors and antennas and many of them are reluctant to risk trouble with the FCC about interference, even though WiFi operates in “Part 15? of the unregulated-regulated spectrum. I have found that my new Toshiba notebook with built-in Centrino 802.11b, has no noticeable interference from my hands on the keyboard as is STILL the case with my older Toshiba with an external Lucent-Orinoco card. I have an external, ca. 6? magnetic antenna for that card for use in my van. That makes a HUGE difference in finding and connecting to public WiFi signals. In a coffee shop this is not much of an issue, but if one tries to use a laptop computer in their vehicle, the antenna integrated into the PCMCIA card is usually below the level of the metal body, which SIGNIFICANTLY reduces or eliminates any WiFi signal. If the laptop/notebook is on the dashboard of the vehicle, you will usually see a significant increase in signal strength. The answer is simply to use PC Cards which support an external antenna that you can magnetically stick to the roof of your vehicle. If you would like a card that has a port for an antenna check this link: http://www.netnimble.net/netnimblestore/ and buy the add on antenna. If you use this card you will need to disable your on board Wi-Fi card.