Alternative to wifi card?

I have a 1st generation mac pro, and airport extreme and 2 laptops with wifi.
I initially bought the airport extreme as cable modem was in the same room as the macpro and i don't have a wifi card installed. I have now moved the mac pro into another room without the cable modem so now I cannot connect the airport extreme to the mac pro via ethernet. This isn't a major concern of mine as the mac pro is only used for music, the only internet access it needs is for software updates.

My question is; is the a wifi usb dongle or something similar that I can purchase to connect only when i want to download software updates? I have had some hardware problems with the mac pro which required the logic board and graphics card to be replaced so i would prefer not to go down the expansion card route. Alternatively could I connect my mac pro via ethernet to my macbook pro and access the internet/software updates that way?


Thanks