|I see what you mean now. The digital converter is what we would call in the UK a terrestrial digital receiver to differentiate it from a satellite digital receiver.|
Which type you buy depends on if you live in a good reception area. If you do the USB plug in device should be adequate. However, if your local reception is not perfect I would go for an internal one because then you can connect an external antenna to it. You do need a good signal with digital TV because the drop of from a good picture to total crap is sudden and dramatic. No gradual deterioration like you get with analogue TV.
Hauppauge do a good range of TV adaptors of various kinds. They are pretty good and have been in the business for a while so know what they are doing. Hauppauge is an American company based in New York.
Bear in mind that you will need different equipment depending where you live. Europe and America have slightly different broadcasting standards.
AS for the wi-fi card a quick search of Google will give you some idea of what is available..
Where you buy these things is dependant on where in the world you are.