You don't need four disk partitions to install 9.0.1. What you do need is enough space to install the program files and the seed/sample database. You can stick the seed database wherever you want (one partition works fine for that too).

The multiple partitions come about from Oracle's OFA guidance. The "format" thing you are missing is related to UNIX system administration, not Oracle. Since you say your database is for testing and learning, you only need two directories: one that establishes your ORACLE_BASE (which in turn leads to ORACLE_HOME), and one for the datafiles.

The seed database that is created during installation is a throwaway database. If you have the space, have it installed so you can at least verify the installation and operation of the 9.0.1 program files. The size is WAY overstated for your purposes. You can make your own database that is around 200MB, thereby saving around a gigabyte of space.

If you have other questions, you can email me at [email protected].