airport card signal weak

This all depends on several different things.

1) If the airport card is built into the motherboard, then you will not be able to replace it.

2) If you are getting weak signals only inside Airport terminals and not at your house or other wifi spots, then you might be at a great distance from the airports router. You have to keep in mind that most airport terminals are very open that will allow the signals to be a bit more wide spread, my best suggestion in this case would be to walk one direction, see if the signal increases or decreases and then adjust your location.

3) If in the end it is just a bad wifi card then I would agree with your assumption to buy a USB wifi adapter. You will need to make sure you disable your current wifi driver that is on your laptop or you could run into several issues. I would also like to suggest that if you are going to do the upgrade, then buy a “n” network compatible wifi card. This is the newest 802.11x band which gives you stronger and faster wireless connections (That is if the router is an “n” network as well). I myself use this one($26.00): http://www.newegg.com/Product/Product.as...