If you are at all serious about learning more than a few phrases then you must learn the Thai letter system (alphabet) NOW. Don't put it off until later. This and the tone rules will make it much easier to learn new words and their tone. Furthermore you will be able to read books, signs and maps and continue learning much faster. Don't waste any time with books that use novel transliteration schemes when you could be reading the original text without any unambiguous pronunciation.