I'm not familiar with the Rosetta Stone, I'm afraid.
I think it is generally hard for native English speakers to attain another language by living in Europe for shorter periods, simply because too many people speak English, and will jump at the chance to practice their foreign language with a native
This especially goes for the North of Europe, where not being able to converse in English is definitely the exception.
If you need to speak a language to communicate I think you learn much faster!
I'm too much of a chicken to learn that way though. Moving to France and having to depend on my horrible French skills sounds like a nightmare
But I bet you I'd know a heck of a lot more after 6 months. The trick would be to avoid the other foreigners I guess. I think you would naturally gravitate towards people you could communicate with more easily.
It's dawning on me now that what I just described as my worst nightmare is exactly what I put Nicholas through at age 3, when we sent him to English nursery with a pat on the shoulder and a "lykke til" (=good luck)
He knew two English words; "no" and "nose". After a month he understood almost everything they said to him, and after two months he spoke in broken sentences (leaving out the words he hadn't yet mastered) and after three months he could communicate without much trouble at all.
Maybe I should move to France...