Even though you didn't learn much in your French classes in middle school, that varies depending on the teachers and the curriculum. French classes in elementary and middle school in general aren't designed to make a kid fluent; they're more of an introduction to the language.
You might be able to speak with people using a computer, but where exactly would you find them? It's not as if there's a common area where people who want to practice speaking Japanese with each other can do it. Even then, are you speaking with someone fluent or someone just as inexperienced? Because if it's the latter, that still doesn't mean the two of you would catch all of the mistakes going on. If you take a class in Japanese, in two years (along with learning some slang), you probably wouldn't have too much of a problem trying to pick up a woman in a bar.
There's also the case with writing. Even though Hiragana and Katakana can be picked up in about a week or two, Kanji is a completely different story. To be considered fluent, you have to learn about 2000 total. Even then, the way they're hand-written is often different from the way they look typed. Unless following a curriculum or studying through textbooks, there's not going to be an easy way to transition into that. The same goes with speaking patterns, as native Japanese speakers will be able to tell you what syllables to stress in worRAB and how to fix an accent.
The thing is, even a college course in Spanish seemingly might be the better route for you to go as well. School semesters last about 12 weeks, and I'm relatively sure most students learn more than just the basic "how are you" stuff in two semesters. Though your dedication to learning by yourself is pretty amazing, the title of the thread is "Best way to learn Japanese." HellCat is still young, so I would advise him to look into the matter of whether or not there are places nearby that offer the classes. Notably, community colleges--they're more efficient cost-wise.