have a look at
Automated Home - Home it's a UK based home automation site and has a wiring guide.
To give you the info that I think you're looking for.
You need to cable to the following locations:
Media points i.e. where tv's or audio equipment would be in each room
Wall boxes: for control of volume or similar
ceilings for speakers possibly walls as well.
if you flood the house with cat 5e thats capable of handling pretty much all signals with the use of converters/baluns.
speaker cable to all ceilings and wall points and you'll be able to run in the future the last bit with minimal hassle.
consider also do you want intelligent lighting? if so then consider running mains rated cat5 to light switches. Also consider star wiring all lights back to the consumer unit instead of normal ring wiring.
ct100 coax is useful too to each of your possible tv points.
With this approach you don't need to have any clue what hardware you're going to end up with. You just need to think of where you might have anything that might need connectivity so thats wallboxes, comms areas, tv's etc.
As a guide for your main lounge area with tv etc i'd reccomend 10-12 cat 5 connections. a minimum of 4 to 6 cat 5 for each bedroom but more if possible. You can run HD over cat 5 but it uses two cables so what can seem like a lot of cable can quickly get used up.
You can also use cat 5 for infra red distribution for remote control from around the house.
Finally you need to specify a central location for your equipment cupboard.
Ideally this would be a reasonable space that could house pc's, amps, sky boxes, network switches etc etc
Cheers and good luck
Noel