My opinion:

Conversation level spoken Japanese will be far effective. For that along with Rosetta Stone, you should use audio tutorials (like Primsleur's Japanese). They will really help you A LOT.

Script wise, you will, at one point, have to learn all of them. Perhaps, you can start with Romanji so that you understand the language. Hiragana + Katakana + Kanji are important, mind it.  If you ARE serious (as I am), you can take up Japanese classes. The thing about Japanese (or any other Language) is that you learn a lot more when you are being taught by someone. The key is interaction.