How big is the difference between Spanish spoken by a Mexican versus a Puerto Rican?

Can somebody PLEASE tell me the difference between the two dialects? I want to learn how to speak Spanish, preferably the Puerto Rican dialect, but i can't find any specific program for it. I assume the the difference isn't that large, but some friends of mine ( Puerto Rican) argue that the difference is huge, were they being racist? Probably, but i just wanted to be sure before i wasted hours of my life studying the wrong language. Also could you recommend a good language learning program? I would just go with Rosetta Stone,but they are real expensive. Im willing to make the investment,but if i can save $400 bucks going with something just as good( or even better) that would be awesome. Thank you and take care.