... continuing from above:
Case 1: New DB server, existing Enterprise Server, existing environments
Case 2: New DB server, existing Enterprise Server, new environment for testing
Case 3: New DB server with application server, existing environment
Case 4: New DB server with application server, new environment
Case 1 - The simplest case. When you migrate the data, make sure the user names and passwords for PRODDTA, PD7334, etc. are the same on both servers. After that, you only have to modify the existing data sources to point to the new DB server for whichever environments you moved over. For example, if you moved the PY7334 environment, including business data and the path code, then you'd modify the data sources for Business Data - CRP, Control Tables - CRP, Central Objects - PY7334, and Versions - PY7334. Don't forget to modify them in both the System and the Server Map. If you migrate to SQL 2005, you'll have to install the SQL Native Client on the Enterprise Server and your test clients, and modify the ODBC data sources accordingly. If you migrate to Oracle, you'll have to install the Oracle client connection software to the same places, but eliminate the ODBC entries since Oracle doesn't use them.
Case 2 - Migrate the data, and create new data sources for both System and Server Map. If you migrate to Oracle, you'll have to reverse that order, since you'll need the new data sources as the targets when you run R98403 to migrate the data. Other parts of Case 1, talking about installing the database client software and modifying ODBC entries still apply. There are a few white papers around, at least one each on Knowledge Garden and JDETips, on how to create a new environment.
Case 3 - This time, you will need to install the Enterprise Server CD. Install just a minimal set of files as you will be copying the most current set from your existing Enterprise Server. You'll need to create an "Add A Server" Installation Plan (directions can be found in the installation manual) to define the new Enterprise Server. I suppose you could do it manually, but I think it's easier to run a plan through Installation Workbench. You'll also need to create a new database as the Server Map for the new Enterprise Server. Since the System database is likely still on SQL 2000 initially, you'll have to install the database client connection software on the original Enterprise Server, and create ODBC entries for SQL 2005.
Case 4 - All the work of Cases 2 and 3 together.
These are merely sketches meant to give you an idea of what the process will involve, whichever scenario you choose. Some of the work (especially environment creation) can be done in advance of the data migration. While you may wish to identify the new data server to ERP 8, it is not necessary to do so if it will only be a database server.