Oracle 10 xe; backing up oradata folder enough to recreate a duplicate later?
List of files that you should backup:

select member from v$logfile;
select name from v$datafile;
select name from v$controlfile;
select value from v$parameter where name ='spfile';


If the last query returns nothing, backup %ORACLE_HOME%/database/initXE.ora (Windows) or $ORACLE_HOME/dbs/initXE.ora (Linux, Unix).

To make it a simple as possible, you can simply copy these files after the database was shut down.

An online backup requires ARCHIVELOG mode configured and using user-managed backup from SQL*Plus combined with OS commands, or RMAN.