The following link should answer all your questions about where to find live coverage of the 118th running of the Boston Marathon.
Live Coverage information
If you want to see it up close and personal, here is a spectator's guide you can download, full of great info and a course map.
And if you need inspiration to qualify for the Boston Marathon, or run your first race, or just some encouragement to keep running as you are, check out
MY BEST RACE -- 50 runners and the finish line they'll never forget.