Hi HomerJ,
The answer to your question isn't straight forward. Although technically it is possible, it is not the best recommended situation to do so. As by having all of the projects DB components on the same DB server offers no safeguard against the different servers connecting to the wrong server and overwriting the project information in the DB component (yes the repositories would be separate, I am assuming that you aren't also wanting to host the different versions on the same app server as that is not possible).

If you are attempting to do this, the things you must take into account is make sure that each qcsiteadmin_db component is unique. The standard installation name is qcsiteadmin_db for all versions. If you are choosing to install all on the same DB server/farm, then I would recommend you use some descriptive name to identify the individual version's qcsiteadmin such as qcsiteadmin_db (ie qcsiteadmin1152_db or something of that sort to identify the different qcsiteadmin db components should you need to back up or remove a certain version and not interrupt the other versions.

Also you need to be careful that you never repeat/ reuse/ or duplicate a project as the DB component name would be the same as an existing and could either rewrite the component or overwrote/ corrupt the component. You will need careful planning to separate the differences ion the projects and versions and insure that the versions don't interfere with other versions.

As you can see what you are asking and attempting is not a good design or plan for modularity and ease of migration, archival, and maintenance procedures.

I (and HP documentation and support) would recommend against such installation and recommend a separate and distinct application and db server for each different version and individual environment (meaning the same applies to the same version duplicate installation, such as a production and test environment).

I hope this helps clarify the situation, that although it is possible techincally, it is not a recommended or accepted practice to set up your various version environments connecting to the same db server components.

Thanks,
Dan