How to start learning Cantonese?
Old post, but those answers make the language hobbyist in me cry, so... 
Are you willing to pay for the privilege? If you are, I recommend Complete Cantonese from Teach Yourself, Basic Cantonese from Routledge, Colloquial Cantonese, and if you want something fun to start with then the Berlitz Cantonese phrasebook with CD. And a heads up, you want something fun to start with.

Basic and Colloquial don't have Chinese characters but the Berlitz phrasebook does, Teach Yourself can escalate a tad too quickly for my taste but it's pretty comprehensive, so between them there's enough overlap and different strengths to give you a reasonable course.

Berlitz into Basic into Colloquial into Teach Yourself would be the easiest order in my opinion, though Berlitz into TY could work. I started with TY and wouldn't recommend it unless you felt like a challenge, though you'll likely progress a little slower even if you do. Each chapter introduces vocabulary, the next chapter uses it, and they stop translating into English after a few chapters; hence why the other books go first. 

You could also go Berlitz into Basic/TY, or Berlitz into Basic, into Colloquial/TY, as using TY along with Colloquial would be much nicer and you'll have a reasonable foundation to build on. It will still be challenging, just not 'lead weights strapped to the ankles while swimming over the Mariana Trench' challenging.

You obviously don't need to buy them all at once, so it shouldn't cost too much in money up front. Just time.