I was at CompUSA yesterday and they have the Buffalo PCMCIA cards that you can attach a pigtail to and then an external antenna.
I have no idea how well they work as I have never used one but this is a possible solution. I am sure there are others as well.
BTW, for all who need to know what EIRP is, here's an article explaining it.
I am not sure if there is anyone out there measuring this though so I don't see why it would matter.