cabling for home cinema/tv set up

I'm about to install a wall mounted sony bravia in my sitting room. Cables from the tv have been preinstalled (in conduit in wall and plastered over) and run to a corner in the room where I have my sky box, dvd etc.

The cables which run from the tv to the corner are as follows;-
1. scart cable for sky box
2. HD cable for DVD
3. Audio visual cable (a green 6 core cable, 75 OHM) - not sure what this will be used for
4. Another cable (7 core, 100 OHM) - I think this meant to be a spare.

Can someone explain to be (I'm a total novice when it comes to this stuff, as you can probably tell), what 3 & 4 are for above??

Now, say I want to install a 5 speaker home cinema kit. The unit and subwoofer will be located in the corner of the roof. If I'm to have 3 speakers around the TV - is there any way of using the cables I have above to save having unsightly cables shown for the speakers?? If I can't use existing cables for the speakers - can someone recommend an appropriate home cinmea system to suit.

Sorry for the all the questions

Do you have a HD DVD player? Can you locate the surround sound receiver close to it? If so, you can connect the DVD player to the surround sound via an Optical cable. Leave the HDMI connection from TV to DVD, this will serve the picture function only. Optical cable will deliver the sound. Unfortunately with any 5.1 surround sound, cabling is inevitable, but you can conceal them along the skirting board.
If you don't fancy all these cables, have you heard of the . Expensive, but I have read good reviews.