please help us!

Our firm is a Financial&Tax consultant dealing with taxation and all other fianacial consultancy work. We bought a building with four floors including the ground floor.Each floor of this building is 20 metres end to end and the floors are connected by stairways. In this building we’d like to have nine PCs in each floor in a networked environmentto take care of all customer needs.How should go all about this. please give us some advice on networking OS and hardwares. if possible, send us your e-mail please.
Rec:Managing director
address:bokeri@hanmail.net