Before I got into all that, I would look into grabbing a good wireless router and running it as a repeater first. It will grab the weak signal, amplify it, and give it to you faster than you can now. I have found that usb network devices have limitations, or maybe they just "feel" slower.
Grab a good dual band draft N router, and look up how to set up a repeater. once that is done, you can then hook it to your pc via ethernet for the win.
