The small lead supplied with the laptop is a S Video to phono converter. The S Video socket outputs the video channel to the TV and the type of lead reqd depends on the available inputs on the TV. If you have a s video input then buy a cable with a s video plug on each end, the audio channel comes from the headphone/audio out socket so you'll need a stereo minijack to phono lead.
If you only have scart inputs you'll need a s video cable that has a phono plug on one end, this together with the audio phono plugs connect to a scart plug that has phono sockets on the back. These cables can be bought from any decent electrical retailer.