either get a pctv card or go to google and search for a site call streamtvnow that usually has all the pay per view boxing and stuff on and its $3 for a month not bad at all really and they are all good quality streams
If your on about streaming TV and all this nonsense about having 1000's of channel dont bother... Most of them are just very low quailty streams.
If your on about Digital TV ie Freeview then this is totally possible with the use of a DVB-T PCI/USB. They range from £25 - £130 (twin tuner versions) but this willl let you get all the freeview channels in digital quality. Hope this helps.