I’ll second S.Anucha’s recommendation of “Thai for Intermediate Learners” by Benjawan Poomsan Becker. I’ve never seen “Thai for Beginners”, but if it’s anything like “Thai for Advanced Readers” or “Thai for Intermediate Learners” then it should be good too. I would also recommend picking up a copy of "Culture Shock! Thailand." It won’t help you with the language, but it will tip you off on how to behave so you don’t make an ass of yourself. Later after you learn to read the Thai script, pick up a copy of “Thai-English Student’s Dictionary” by Mary R. Haas. This dictionary probably hasn’t been updated in several decades, but it’s still the best.
There are a few online resources you should look at too.
LearningThai.com is a really great site that I’ve found usefull and so is
Thai-Language.com. Also the
Nation posts
Speak Thai Weekly which has dialogues for practice, but it wouldn’t be to much help for you until you have a reasonable command of the basics.
I can’t recommend much about KrungThep though. I only lived in the north and east coast and only went through the capital for day trips and such.