Yes, you must install BIM Server (BS) to use Teamwork ... BS manages all files and communications.
However, BS does not have to run on its own machine in a very small office. If you only have a couple of users, it can run on somebody's (very well-equipped) workstation. It is not 'server' software per se that runs on a 'server' OS / computer. However, speed would be severely impacted if BS ran on one machine and the files were located on another file server (PPC or not) on the network - so do follow the recommendations here:
http://www.archicadwiki.com/Teamwork/BimServerConfiguration
Karl
One of the forum moderators
AC 28 USA and earlier • macOS Sequoia 15.2, MacBook Pro M2 Max 12CPU/30GPU cores, 32GB