[Harold]

Five months?
I started back in May and here I am in December, holding conversations in ONLY Japanese (with the help of my dictionary and kanji book, of course).

Five months is more than enough to get the basics down, if not the bulk of the language (grammatically speaking). The only place I think you'll come up short on through self study is conversational skills. I can read and write pretty well, but when it comes down to actually talking... Well, I studder all too often and it takes a while for me to spit out a sentence. If you can, try to get audio CDs to go along with the book, if any. They'll really help you get down the hearing part of Japanese.

頑張って！