It depend on your TV and your PC, but i think it your case you need:
mini PL at one side (computer line out)
one RCA if your TV mono
two RCA it your TV stereo
It is a cheep and common cable you can get it any ware.
If you have modern TV with VGA/HDMI/DVI....you can have better quality.
Only HDMI can carry sound and video on the same lead.
Depending on your PC, as Ark says, you'll need probably a mini jack (like a headphone socket) to RCA (the old-style phono leads) lead, you'll probably have a set of three RCA plugs on your telly - yellow one may be using now which carries the video, the red and white ones are for the sound. Unless you are using HDMI, you will need this separate lead.
HDMI allows for a much better quality (it is digital as opposed to SVGA analogue signal) display - if your telly has HDMI sockets, you should try to use them if you can. Your pc may only have DVI outputs as well as SVGA - you can buy adaptor leads for them as the signals are compatible and give you the same increase in picture quality (although an adapted DVI-HDMI line won't carry sound). I use DVI-HDMI leads at home as my sound goes off to a separate amp and I never use the telly speakers.
I have set my computer up with the scart lead which carries the picture to the tv (sony bravia) and have taken the sound from the headphone socket to the red and white RCA sockets. They both work fine but on different channels.
sound comes through on ext. 1
picture comes through on ext. 2
Any idea how to make them come through on the same channel?