Do you need a complete network, i.e. running multiple cables from each room back to a central position or home hub? No problem.
Or are you just after getting rid of that trip hazard connecting the xbox live to the router in the upstairs bedroom? In this instance we could help by running a BT cable to the lounge, so the router is in a more central position, then install the cat5e (Network) cable up the room it is needed in. No fuss, job done.
Whilst having other trades in or electrical works consider thinking about running these type of cables in even if they are not needed yet. If you do this it may be worthwhile making a note of their location, so if you sell the property, the new buyer is aware they exist.