As a professional interpreter, this really made me laugh! Thai is not one of my languages, but we do have a Thai "Ba". My 13 year old son has the tones down MUCH better than I do. On our last trip to thailand everyone seemed to understand him but when I would ask how much something costs I would just get a blank stare.....until my son would ask the same thing and get an immediate response.

Good luck with whatever method you choose!

Forget learning the language for a short period (advice from someone who speaks 6 other languages and has a Thai wife :) ). English will do you just fine. Just learn few phrases, like Hi, Thank you ...

Chai = yes. Can also use "Krap" (meaning "OK" if you are male), "Ka" if female.
Mai = no

If you are male:
Sawadee krap (Hi)
Khob khun na krap (Thank you)
Yindee krap (You are welcome)

female:
Sawadee ka (Hi)
Khob khun na ka(Thank you)
Yindee ka (You are welcome)

Chai means 'correct'. For yes a simple acknowledgement with krap suffices.

Technically speaking there is no Thai word for yes.

Try uttering chai after someone gives you directions and see how much it confuses them. ;)

Well, it's just a flavor, which I think is somehow obsolete. Maybe it depends on the region, but my in laws use "chai" to answer questions that require yes/no answer. They use 'ka/krap" more like some sort of confirmation.

I don't think anyone will be confused if a farang uses with "chai" for "yes".

You would certainly be safe to use 'chai' when the sentence ends with 'chai mai' [as that specifically seeks a yes/no answer] but krap/klap is universal for 'I agree/yes/yup/okay/I get it/uh-huh'...heck, properly/politely you're probably even hear 'chai klap'--krap pom is even better when talking to police or immigration :) The "Help" section of Talking Thai doesn't really distinguish between chai/krap but it does offer polite/formal/slang/verboten versions of common words and that really comes in handy. The Help section is really a grammar/spelling/alphabet guide-tutorial and it links directly from each word if desired. Even covers tougher things like interpreting silent letters...