It is possible to use a repository DB, either on the server where you want to install HP OpenView Service Desk, or on another server. It is a clear description in HP OpenView Service Desk 4.5 Installation Guide: Create a SQL Server database, page 44 - 47 Database Configuration, page 82 - 94 Configuring the Application Server, page 124 - 139 For some problems we will try to assist you.
install the client and server software on the system. During the server software instalation you will be asked for the details of the database. As long as you have connectivity to the database from the system it should be fine.
If you have an existing OVSD application server installed then you launch the Openview Server Settings Editor from the start menuabd set the database details there.