OK, this is hardly an OCUK query but I don't know of a good DIY forum 
I want to lay (semi)permanent Cat5 between my geek room and my living room. They are on the same floor but staggered doorways across a hallway. I can't go under the floorboards as there is a downstairs neighbour (or can I??), but the floor above is also ours, as is the loft (3 storey townhouse thing).
My immediate thought is to try and get the cable behind the skirting boards, which should be easy. However I've no idea how to cross the hallway! I think the proper way to do it is go up the inside of the plaster to the loft, cross over to the living room, then again drop down behind the plaster and out the skirting. However this seems to be a difficult and long (meteres) job!
Really, I don't want to break anything or have to do any redecorating. I certainly don't want to be drilling holes through underfloor joists. Is it possible? What is the norm?

I want to lay (semi)permanent Cat5 between my geek room and my living room. They are on the same floor but staggered doorways across a hallway. I can't go under the floorboards as there is a downstairs neighbour (or can I??), but the floor above is also ours, as is the loft (3 storey townhouse thing).
My immediate thought is to try and get the cable behind the skirting boards, which should be easy. However I've no idea how to cross the hallway! I think the proper way to do it is go up the inside of the plaster to the loft, cross over to the living room, then again drop down behind the plaster and out the skirting. However this seems to be a difficult and long (meteres) job!
Really, I don't want to break anything or have to do any redecorating. I certainly don't want to be drilling holes through underfloor joists. Is it possible? What is the norm?