Hello yosi,
The windows support mostly included in master, but its missing the reboot feature. That is still under review and soon to be merged. After the final branches merge, you will be able to safely reboot the system via your charm.
Until that merges, you will be able to run simple charms that do not require reboot to finish. The target release for windows inclusion in juju is 1.21. right now, version 1.21 is in alpha2 and is planned to be released in the next couple of months. Until then, if you are feeling adventurous, you may follow the wiki page ayrton posted above.
If you run into any snags, please feel free to post a followup question, or ping me on irc (freenode). My handle is gsamfira.