I started doing the smart coach on runner's world, but never went thru it. I'm not crazy about it, because it was hard to follow with my schedule (full time work with 2 young children!). I would definately recommend trying visiting it though.
Personally, I'm hoping to do a half marathon this year as well. I'm just planning on upping a mile every couple weeks and doing strength exercises. I'll occasionally on my busy days doing more of a speed thing, but I could care less how fast I am too!
WHich one are you going to in May? I considered the Illinois Marathon, since it will be flat, and I went to school there