Step by Step - Uninstall Oracle 9i

Go to Oracle Installation Products from Programs - Then Universal Installer - Then follow the screen shot.

Click Deinstall Products

Select All products

Select All products by clicking all the above. Then Next to uninstall.
Click on "Remove" and click "Yes"
once it finished click "Close" and then "Exit"
You may manually interrupt to remove other directories and services related to oracle.
Step I to check:
Stop any Oracle services that have been left running. Go to Start > Settings > Control Panel > ServicesOR Go to Run Then type services.mscServices may be 'OracleOraHome90TNSListener' and 'OracleServiceORACLE'. Generally service starting with 'Oracle'.
Step II to check:
Run regedit - Start Then Run Then type "regedit", click "Ok"Delete the following keys:HKEY_LOCAL_MACHINE \SOFTWARE\ORACLEHKEY_LOCAL_MACHINE \SYSTEM\CurrentControlSet\Services\EventLog\Application\Oracle.oracleHKEY_CURRENT_USER\SOFTWARE\ORACLE
Step III:
Delete the Oracle home directory:"C:\Oracle" or "D:\oracle"
Above will remove database files:
Step IV:
Delete the Oracle program Files directory:"C:\Program Files\Oracle"
Step V:
Delete the Oracle programs profile directory:"C:\Documents and Settings\All Users\Start Menu\Programs\Oracle - OraHome90"
Step VI:
You may also need to check the below:
To remove these: Start > Settings > Control Panel > System > Advanced > Environment Variables, See the system variable 'PATH' and edit them to remove any references to Oracle.