If you go, for instance, to the BBC website, you can watch programmes live by going to the relevant page link. For example, BBC News:
You'll see links to other channels on the left and, on the right, the On Now button.
You'll have to install the BBC iPlayer first.
Another way is to download an application such as:
I have it installed and occasionally watch some of the foreign channels, but it can be a bit hit and miss.
Best method, to be honest, is a good Freeview TV PCI TV card...:-)