I installed the GENGO plug-in no problems:)
I was able to run ut successfully on my test wordpress blog. For a number of reasons, though, I opted to create two blogs for my two languages, instead of one (for full control and freedom how both blogs look and feel).
But yes, Gengo works and is pretty nice plugin!
If you have a theme translated in two languages (.po/.mo files), Gengo will correctly switch the languages on your blog when you post in one or the other language:)
Head for the gengo forum mentioned above, and also you might find some pretty good info at:
Cheers, my $ 0.02, Michel