Decide which learning style will best suit your needs. Because you are not learning Portuguese in a strict classroom environment, you can choose from a more visually based learning system, such as Rosetta Stone or Babbel, or a site dedicated to vocabulary building based on reading.
Enroll in a Portuguese course offered online through a community college or a university if you are seeking college credit for learning online. You will not have to attend classes and can learn from the convenience of your home.
Visit a virtual world that has lessons and voice chat that enables you to talk to native Portuguese speakers through the internet. Second Life offers courses through different universities in-world that will allow you to speak and chat with others who are also studying Portuguese. (There's a link to the "Portuguese Republic" in Second Life in the Resources section.)
Take a trip to your library and see what is available for study. Oftentimes, libraries will carry Rosetta Stone and other visually-based learning programs and will offer slots to sign up and take lessons on their computers.
Download an app to learn Portuguese on your phone or your reader. Dummies, the iPhone, BYKI all offer virtual learning by simply purchasing an inexpensive app to help you with vocabulary, grammar, and pronunciation.