Ok, now, after a lot of time and trouble I found the final solution. I located the file where the resolution settings are stored.
There you can configure any resolution you like. Also 16:9 and 16:10 resolutions.
The file is called 'pinata.cfg' and is located in
C:Documents and Settingsyour-usernameLocal SettingsApplication DataSaved GamesMicrosoft GamesViva Pinata
or in german XP
C:Dokumente und Einstellungenyour-usernameLokale EinstellungenAnwendungsdatenSaved GamesMicrosoft GamesViva Pinata
Pay attention, the path and the file are normally hidden, so you should enable your explorer to show hidden and system files.
In the file itself just adjust the first 2 lines to match your desired resolution:
videoscreenresx = 1440
videoscreenresy = 900
Dont forget to save the file though ^_^"
GL & HF
overreaction aka El_Cangri aka Carlos