After years of haphazard cardio training I've just treated myself to a turbo trainer and heart rate monitor. Does anyone have any training programs or know any good websites that could help?

Go to the library,thats what I did,you can usually find a few good traing manuals,I've got Cycling for Fitness by Dave Smith which gives good advice on starting off with cardio training.The best advice is to do steady endurance rides through winter(60-80%MHR) and then coming to race season add some high intensity training(1 a week,2 max at 85%+).Watch the high intensity stuff though as its easy to overtrain.

I find that steady endurance rides are really really dull on a turbo trainer. i find it easier to motiviate myself to do intervals on the trainer. it hurts more, but time seems to go past faster.
psychologically i find, "thats 2 sets done 4 sets to go" easier to deal with than " keep doing this for the next hour"

try here:

http://www.jbst.com/i-Coaching-2002.html