No, the ObjAcct Suite can be installed on a separate server.  It is linked to Astra Schedule via a URL.

ObjAcct requires that it be installed on a machine with an MSSQL Server (or SQL Express) database.  Additionally, IIS is required because the web service is necessary for the interface between ObjAcct and Astra Schedule.  If another machine is available that meets these requirements, then there is no other reason to install the ObjAcct server on the Astra Schedule application server.

Server:

2.0 GHz, 1GB, 40GB, Server 2003, 2008, XP, Vista

Workstation:

2.0 GHZ, 512MB, XP, Vista

Database:

SQL Server Express, 2005, 2008