Some very nice training plans by the Garmin folks can be found here.
Best of all … you can upload those training plans to your garmin watches !
Triathlon plans are divided in Beginner and Intermediate for the sprint and olympic distance
Marathon plans are divided in Beginner, Intermediate and Advanced
http://gbr.garmin.com/winter-training/en/plans/training-plans.html
Please be so kind to click on an Ad if you find this information useful. It allows me to keep buying those nifty tech tools :-)
thx,
Gert