Unfortunately, a standard TV tuner cannot tune in satellite TV broadcasts. What you will need is a Satellite DVB-S Tuner as chef mentions. If you are happy with the free channels you can get without putting the viewing card in your satellite receiver, then a very basic DVB-S tuner will do fine such as the popular Skystar2 card, which typically costs around Â£60.
<img src=“http://upload.cdfreaks.com/seanbyrne/PCSatReceiverDish.png” align=“right”>As you mention you have a Quad LNB (I assume you mean Quad-output), this should be sufficient for connecting up both your Sky satellite receiver and a DVB-S card to the same dish. Note that unlike TV aerials where you can connect up multiple outlets to the same cable, this cannot be done with satellite unless you intend only operating a single device on the cable at a given time. Even in this case, you would need either a priority or AB switch to prevent the power supplied down the coaxial cable by one receiver from causing problems or possible harm to another tuner device connected to the same cable. What you will need to do is bring a separate line from each output of your LNB to each appliance. The example shown to the right assumes you have a Sky+ Digibox as this requires two dedicated coaxial cables from the dish. For a standard Sky Digibox, only a single dedicated cable is required for the Digibox.
For picking up channel 4 & 5 (note that ITV 1-4 are now free-to-air), you will need a suitable DVB-S card with a CI slot (typcially from around Â£100 up), a CAM capable of supporting NDS (varies from around Â£70 to anywhere over Â£100) as well as your existing Sky Viewing card. There are no official NDS / VideoGuard CAMs as from what I’m aware of, support of this encryption system can only be obtained with the content provider’s proprietary receiver. There are CAMs where ‘NDS compatible’ firmware can be loaded on such that you can use your official Viewing card in these, however as Sky is against the use of non-Sky hardware to tune in their broadcasts, I would not recommend forking out on an expensive DVB-S card with a CI, not to mention the cost of a suitable CAM, especially if you are just looking to watch these two channels.
For a full list of free-to-air channels on the satellite Sky broadcasts over, have a look at the following frequency chart:
Channels listed in bold-writing in the faint peach colour are free-to-air TV channels. Channels listed in plain-writing in the same faint peach colour are free-to-air Radio stations.
The following link lists the channels which are free-to-air or free-to-view (requiring FTV card) as well as what category of content the channels show: