Starting to Learn Greek

Since I started my vacation about 2 weeks ago, I have been trying to teach myself Greek. I have a book which is OK, but not very rigorous. I have promised myself that if I can make it to lesson 20 in this book, I will spend the money and buy Bill Mounce's textbook and workbook. If I can't make it to lesson 20, then it would be a waste of money to buy another book. I'm in the middle of lesson 8 now. Why is it not rigorous? Well, it has introduced verbs and has presented some conjugations, but at this point I have no idea whether Greek verbs have a regular conjugation, or whether I am just learning a special case. Anyway, it is interesting. I've also made up some flash cards, which my 7 year old can help me to drill with. She'll enjoy teaching Daddy!