using a switch as a network repeater

Hi,

I have a company planning to upgrade to gigabit ethernet, they have a main floor where most of their connections will be used and a second floor where they need about 6 connections,

however its over 100m in cable length to get to the second floor, would a 12 port unmanaged switch support 6 simultaneous transfers at full speed and act as a repeater for those 6 lines?

if not what is the best solution to this problem?