Training overload

So yesterday at lunchtime I did an hour on my bike...one I borrowed from a wonderful neighbor and now need to get used to. I have done all of my previous events on a mountain bike, albeit a very nice one, but it still took too much energy to use it in events. Im hoping that this bike will allow me to shave a few minutes off my time, while stopping me from exerting as much effort as my MB did so I can survive the run. After biking, the plan was to run for at least a little while to get used to the jelly legs and be ready for Sunday...but I made the mistake of checking my work email and that was that. Besides, I figured I could run after Masters Swim last night and get a good idea of what is will be like to run when exhausted from an hour of swimming (and probably still have jelly legs). I made it to the treadmill after Masters, but elected to walk a 1/2 hour instead of run due to a little knee pain. I want to make sure I make it to the start, so I might just have to take it easy this week. I know I can do this, right?