I want to help people who need Google +1 button and who use SMF 1.1.14. I took a Google +1 button code from http://www.google.com/+1/button/ . Then I just paste it in our headers. And now it's working and looking very well (if you want to see it: http://www.seo-forum-seo-luntan.com/index.php). Hence all you need is to take the button code and to paste in your headers (in a place you like).
I hope that this information will make a lot of SMF fans happy. Good luck to our community, dear people! :)
Right now I saw that there is already a mod for our 1.1.14 versions:
http://custom.simplemachines.org/mods/index.php?mod=3103
May be some guys will prefer to use this kind of mods. Anyway. Good luck!