In an enterprise environment, DBAs will have the responsibility to install software including the one you mentioned (the database software, Developer 2000 Forms & Reports 6i Forms/Reports 6i/9i/10g, Oracle Discoverer EUL or Discoverer Server 4i etc…, assuming you are only interested in Oracle products and related products such as Toad.
Programmers do not get involved in installing or setting up software programs. Programmers just develop software application programs (front end) including Forms, Reports, Discoverer, XML applications. They also write code for the backend (database) and the front end (applications). They also perform customisation tasks.

Most companies would install Oracle databases and Oracle ERPs on Linux or Solaris platform, which is more stable and more secure than Microsoft platform.

Software like Toad, SQL Developer and Developer 10g are installed on windows platform on the client machine.

For learning and practice purposes, I would advise you install Oracle database, Forms and Reports 10g on your Windows XP. Oracle Forms and Oracle reports connect to Oracle Database. You may have to do a small configuration on Listener.ora and TNSnames.ora text files to provoke the link Forms and Reports 6i/9i/10g to Oracle database.

You don’t have to install SQL Developer separately when you already have Oracle database or Oracle Forms or Reports 6i/9i/10g installed.

If you install Oracle Apps 11i or Oracle Apps R12 on Windows platform, you will automatically have installed, Oracle database, Oracle Vista database, Oracle Forms and Reports 6i, Oracle Discoverer 4 EUL and Oracle Discoverer Server 4i, etc… I don’t know how it is when you install Oracle Apps on Linux platform.
I hope this is informative to you.

Cheers,
Gavrobere