Hi Mugambi,
I've known "medium-sized" offices with 10 people and with 200 people, so
that's not very helpful.
Also, strictly speaking there's no such thing as an Access database. By
default, Access uses the Jet database engine that is automatically
installed with it, but it can also use industrial-strength server-based
databases such as SQL Server. And the limits in terms of numbers of
users, volumes of data, and so on are mainly set by the database engine,
not by Access itself.
If you have sizeable data processing needs (e.g. gigabytes of data,
tables with many millions of records) Jet is not suitable, but Access
properly set up with a suitable SQL Server back end can handle it - for
any number of users from one or two into the tens of thousands.
If the volume of data is not going to exceed a few hundred megabytes,
and only a few users will be actively updating or querying the database,
and they are all connected via a good wired LAN, Access+Jet is just
fine.
If that description is correct now but may change later, use Access with
the MSDE database engine that is also supplied with it. This is a "lite"
version of SQL server, so makes it easy to scale up to full SQL server
later on.