If it works for you get onscreen keyboard software, not sure what is available (I have a tablet PC with this technology). The advantage is it works like a full sized keyboard yet you dont have to lug it around. The disadvantage of course its not a full size keyboard. Pending the size it may be helpful to get a stylus from your local office supply store.
If you want a real like USB keyboard, just browse around from what I can tell keyboards are basically keyboards, if it works for you it will work.
If you want wireless, I couldn't reccomend the Logitech MX Duo setup more, though it requires a plug so would be more difficult for CarPC setup.