I despised the Rosette Stone - primarilly because of the high price. I tried it out on a friend's computer, as she had it (her dad or grandpa or someone had bought it). Price aside, I didn't really personally like it and it didn't help her a whole lot (she found it boring as did I).
I would recommend LiveMocha.com (comparible to the concept of the Rosetta Stone, but free! And an interactive community of real people!) and How-To-Learn-Any-Language.com (yes, that ridiculously long thing IS the URL).
Don't forget translation/dictionary sites like-
Verbix.com (which will provide you with a list of all the conjugations of a verb, which is useful when trying to look up a verb, but don't know the infinitive of - though, watch out, sometimes it's wrong.. I think it said "geschehen hat" instead of "geschehen ist", for example, but I'm not really sure if that was it's mistake - the conjugations it gives, however, have all been correct, in my experiences.. it's the helping verbs it sometimes screws up, but I've had official workbooks from German classes that screw these up.)
Other than that, grab a child's book (not a fairytale/Märchen book), a German-English/English-German translation dictionary and a little notebook (of the paper-kind, not the electronic portable-computer kind) or self-made flashcards for vocabulary practice. Always, and I cannot stress this enough, always include the article (der, die or das) along with every noun you learn - if you don't know the article, then you don't know the noun.
Work on learning how the case system works, so you know the difference between
"Der Hund beißt den Mann" and "Den Mann beißt der Hund", or why products come from "der Fabrik" rather than "die Fabrik".
And remember, a computer is never an "it", grammatically speaking, it is a "he" - even when the Germans call it by the English name (which they do!), it's still a "he". "I hate my computer, he is too slow!", a German would say. A door is never an "it", it is a "she" (die Tür). A girl, however, is not a "she", she is an "it" (das Mädchen - because the diminutive form "-chen" makes everything 'das' - same goes for "-lein", like "das Fräulein").
I'd also recommend reading magazines or books, or finding music you like in German, so you can enjoy your 'practicing' instead of just forcing yourself to do it.
I also read Wikipedia articles in both English and German (often, the German Wikipedia has more information and is better written).