Most software or CDs will teach you the formal French.
I tried Rosetta Stone for Spanish and found it effective for basic sentences or words. But you could not get fluent or reach an Intermediate level with it, especially as there is no grammar explanations. The best way to get fluent is to communicate with a native speaker or live abroad, which is unfortunately not always possible. Rosetta Stone can teach you the basics, but not be really communicate.
Pimsleur is very different as it is audio CDs so you will listen to the language, and then try to repeat it. It is efefctive if it is your learning style. One of the disadvantage is that you don't get any feedback with audio CDs so you can think you are saying it right but nobody will correct you unless you can talk to someone.
Nonetheless, I found another language software that my college was using called TeLL me More. I found it to be less repetitive than Rosetta Stone, but also more effective to communicate. For instance, they have an activity where you could actually have a dialogue with the computer: the computer says one sentence, you have three choices of answer and you actually speak the correct answer (headset and mic is already included) and the computer recognizes what you are saying and moves you on to the next sentence. They have a free trial on their site www.auralog.com . I also found out after buying it that they are better ranked than Rosetta Stone on http://learn-spanish-software-review.toptenreviews.com/. I reached an Advanced level already and feel confident communicating in everyday situation. It has an audio CD which was nice
Learning a language takes time and dedication. If your goal is to learn in 6 months, you should spend several hours a week regardless of the solution you choose.