Hi HomerJ,

Technically yes you can share the DB between two different instances, although it is not a recommended practice. What you would need to insure is that the projects are only in one instance, so if you have two of the same project to be on different instances the naming construct would need to be unique for each instance to insure that the correct projects are being used by the correct instance and it's associated siteadmin. You would also need to insure that each instance has a unique and separate instance of site admin so that the correct users are projects are associated with each instance.

As you can see it is something that although possible would take considerable planning to insure that corruption and unintended changes and usage don't occur. For this reason the recommendation would be too keep each instance on its own separate DB instance, but it is entirely possible to do with the correct planning, documentation, and such, especially since you are using such widely varying versions and the environments they support (DB and OS versions) vary so greatly between the two versions.

Hope this helps answer your question,
Dan