How to install oracle 11g XE and use the data files of another instance (like Postgres)?
I see no reason you can't do this.

Typically, you would perform the following steps.


Move the *.dbf files found in %ORACLE_BASE%\oradata\ to a safe place.
Move the files found in %ORACLE_BASE%\fast_recovery_area\ to a safe place.
Move the spfile found in %ORACLE_HOME%\database\spfileXE.ora to a safe place.
Install a new Oracle instance and
Configure it with oracle-xe configure command.
Shut the instance down.
Move the data files, control file, spfile and online redo log files back to their previous locations.
Star the instance.


You would also need to make sure that you specified the same settings during installation as you used with your previous database (ORACLE_HOME, ORACLE_SID, listener port etc.), otherwise your instance won't start. Ideally I would recommend you doing silent installation with response files (described in Oracle Database Express Edition Installation Guide for Microsoft Windows). This would ensure that you've used the same settings across operating system upgrades/reinstall.