Touchsreen pc's just run an OS, usually windows, its a bit like the old Mac's where all the components are in the monitor (same as a tablet).
Since these are not upgradable like a tower PC where you would get a good PCI tuner card your option is to get a usb tuner and go via that route, just make sure you got a good signal via an aerial and not the crappy antenna they give you with a suction pad. Another note to take on, most USB tuners don't have great software which is not an issue as there's some really good solutions out there, can't remember what I used last!
Another problem with these tuners is they don't have a proper male/female coax input they usually use a tiny connector but you can buy the correct crimps/pins to convert to standard aerial cable to go into it to get the best signal. PCI tuner cards will usually have proper connectors unlike the USB counterparts.
Hope this helps
