If you open up your computer you will probably find that it uses one of a few standard wi-fi cards. They typically have a very small coax cable going them. the cables will be either black or white, some computes use both the back and the white cables (the wi-fi card is well marked to show which cable goes where). The ends of the cable are a press-on coax and are generally gold plated.
A quick search for "long wi-fi cable" on ebay got me this http://cgi.ebay.com/MINI-COAX-ANTENNA-U-FL-JUMPER-CABLE-MINI-PCI-WIFI-LONG-/350288304395?pt=UK_Computing_Networking_SM&hash=item518ecf590b
I know nothing of this vendor, it is just an example.
To get the cable outside of your laptop, you may need to drill a small hole. I am not saying any of this is a good idea; but, it is pretty easy.
You could go with something like this and then you will have an external connector permanently mounted on the side of your laptop. http://cgi.ebay.com/U-FL-RP-SMA-Female-10-Pigtail-Cable-Mini-PCI-UFL-RG178-/110538306742?pt=LH_DefaultDomain_0&hash=item19bc98b4b6
Of course, you will still need to drill a hole to mount it.