Agreed with mryoink. Different offices uses different topology, and you will need to consult an IT personnel and clarify your needs, and your plans so that he can make arrangement and discuss with you further. We cant just define a topology.
I've been to many places, and some uses the Tree, some uses the Star. Well, it still depends on your office layout any future plans.
For your computer wise, are they new or old.. Why are they licensed under windows 95? Just to inform you that win 7 may not be to run on slow PCs. There are too many services and backend security running simultaneously. You might want to consider proceeding with winXP.