Having a highscore list in a game runned from localdrive on a pc.

what is the best options here? write to a tempfile in %temp%/gamefolder, storing in registry? or using a properties file?

hwat options do i have to write files to the drive in Unity api

This is an ideal task for "PlayerPrefs". (see link for the manual page).

PlayerPrefs allows you to store and retrieve data in all types of build (even webplayer) on the local machine, without needing to worry about where it's saved.