I will echo what Dave and Jeff mentioned above. I started running semi-seriously at the age of 36 almost three years ago. I weighed 181 and my pace was 10:30. About two years ago I decided to get serious and I trained for my first marathon at TOU 2008 where I achieved a 4:34. I just qualified for Boston at St. George with a time of 3:11 (see report at
http://jj.fastrunningblog.com). I am also now 34 pounds lighter. In my opinion the thing that will make the biggest difference in reaching your running goals is increasing your number of weekly miles while avoiding injury. Weekly running volume is huge for improving performance. Like Dave said I would not worry too much about speedwork, tempo or intervals until you have gradually built up your base of weekly miles to at least 40 to 50 miles a week. However, you need to do this slowly or you will suffer. I also agree that you should run 6 days a week. Once you are at that level then you can come back to the blog/forums where you will find awesome advice on how to torch your training. My guess is that by then you will probably already be running comfortably in the low 9's to high 8's if not better. Good luck.