I've been using the Workouts feature in Garmin Training Center for my C25K runs. They're really handy for interval weeks, which are a part of Bridge to 10K as well. Grab the TCX files for all of C25K and B210K here:
Import them to Training Center by selecting from the File menu "Import to Current User Account" and then "Workouts...". From there you'll see them in the Workouts tab, and can sync them to your Forerunner. They should work with the Forerunner 205 and 305.