I was looking at some Oracle databases recently and I saw that the Oracle Auditing Tool (OAT) is an awesome toolset but you just need to download the classes12.zip which are the Oracle JDBC drivers for Java into that same directory. I downloaded the classes12.zip from the Oracle site and placed it into the same folder as OAT. On linux, the .sh files will then need some editing. Just replace classes111.zip to classes12.zip and off you go.
Patrik Karlsson has done an awesome job of providing these tools. You can do the whole gamut of operations using this tool from first guessing the Oracle SID to checking for default passwords using opwg.sh.
sudo ./opwg.sh -s 192.168.1.101
The above command will give you the Oracle SID for the remote database.
Once you have the sid and the credentials you can run queries using oquery.sh
sudo ./oquery.sh -s 192.168.1.101 -u DBSNMP -p DBSMP -d db_sid_found -q "select 1 from dual"
The source of the OAT is also provided here: http://www.cqure.net/tools/oat-source-1.3.1.zip. I found an interesting decompiler for Java too (when I overlooked that the sources existed on cqure.net website) and it’s called jd-gui. It works wonderfully on linux.

Sometimes simplest of the errors get you bad….and this was one such time.
I was trying to connect to my Oracle XE DB using SQL*Plus but kept getting this errror

connect hr/************
ERROR:
ORA-01034: ORACLE not available
ORA-27101: shared memory realm does not exist

Turns out I did not start the DB instance.
Start -> All Programs -> Oracle Database 10g Express Edition -> Start Database