Several years ago my local Adult Ed department had a basic Thai class. I took it before my second visit. It did help some. The teacher was a woman from Chiang Mai who had been a teacher in Thailand. The class was very small, less than 8 students. But you can only learn so much one night a week for a couple of hours for 10 weeks. The tones are definitely the hardest part. I never really did understand when I was getting the tone right. She would make us repeat until she heard the tone she wanted to hear but I had a hard time making it stick on my tongue and in my brain.

But I think you can still make yourself understood from the context if you get the word right but the wrong tone. The biggest problem is that if some one thinks you know Thai they will start speaking Thai to you. I can figure out how to say something but comprehending what is said back to me is really difficult.