Is an Oracle 10g instance dependent on the windows account authentication?
Oracle on Windows creates a service for database instances, called OracleService%ORACLE_SID%. By default, this service uses the Local System account so a password change of the installation user will not affect the database.

It is however possible and recommended to change the service user from Local System to a standard Windows account. If you performed this step, and you wish to change the password of that account, you must update the password in the service configuration.

Managing Oracle Home User


  You can change the password using Windows tools. However, when you
  change the password for this Windows User Account, you must also
  update the password for all Oracle services running under the Windows
  User Account.