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.