Unicode is a key for international database development.
You should post questions about international characters in web browsers in their appropriate sections because here are probably not experts which could answer it quickly and accurately. Also Oracle has its own zone.
To test polish environment you may simply look in Control panel Regional settings and set it. Additional info is on Microsoft web (e.g. for Vista it is here:
http://www.microsoft.com/globaldev/vista/vistahome.mspx)