In oracle 9i we have some limitation with reqard to Backing up entire dataabase in one go. First we will have to take the database in mount stage (not open) in order to take the back up and that too one tablespace at a time.
like:-

sql>alter tablespace <tablespace_name> begin backup;

copy all the datafile
querying v$datafile v$controlfile

after backing up the said tablespace End the command as:

sql>alter tablespace <tablespace_name> end backup;

We use alter database begin backup to copy datafile from one location to
another using host command copy / cp (based on environment).

The command is already posted

Alter tablespace < tablespace name >

Begin backup

Copy the datafile to another location

After copy alter tablespace < tablespace name >

End backup;

This would tell database that backup has complete its much simpler if the same
things are done using RMAN.