Can any Buddhist become a buddha?
That's sort of a hard thing to answer. Buddha is just a title which basically means great spiritual teacher of the era, or first awakened of the era or something like that. I'm a little rusty on my scriptures, but from what I remember the original pure message of buddhism needs to fully die out before another buddha will appear and spread the message again (i don't mean that in a theistic sense either, the current buddha was simply a man who had great spiritual insights).
People can however become Bodhisattvas, which are sort of the same thing to a lesser extent - great spiritual teachers who spread compassion. Tibetan buddhist believe that the Dalai lama is one for example.
But again, the buddha said to pick and believe only what applies and works with your life, so there's many scriptures that people don't follow.