[Halcyon]

I also have my broadband point upstairs and have either gone through the ceiling or under the floor boards. Make sure to keep the cables away from your electricity ones if possible.
I've then gone down under the stairs to pass the cables to the floor below.
Make sure you dont bend the cables too much and be careful if you are pinning them down as you dont want to damage the cable.

*** Oh and first golden rule, before you install any long length of cable, test it to make sure it works. You dont want to take it all up again. ***