|If you want to type in Greek - Go to Control Panel>>Region & Language>>Keyboards & Languages>>Change keyboard>>Press Add and select your desired language.|
In case you need to change the display language of Vista to Greek...follow the below steps:-
Before doing this, ensure that you are using a Licenced Vista.
Open Windows Update by clicking the Start button , clicking All Programs, and then clicking Windows Update.
In the left pane, click Check for updates, and then wait while Windows looks for the latest updates for your computer.
If any updates are found, click View available updates.
Select the language pack that you want, and then click Install updates. If you are prompted for an administrator password or confirmation, type the password or provide confirmation.