Training to walk a half marathon is not too difficult, but allow yourself a little time to get used to walking distances without getting blisters. The half training schedule links on this page give you all you need to know to set your training goals.
What Training Do You Need?
Here is a half training schedule (from About.com) for walkers.
If it’s a big race, you certainly will not be the only one walking. And, just so you don’t feel bad, I’ll let you in on a secret. Most of the runners walk at least part of the way, anyway – I know I do!