Disappointed

This is exactly what I love about tri training.  Can't run cuz the knee is sore - swim and bike (if possible).  Can't make time to drive to the pool?  Go for a quick run.  and so on.  There's always something you can do that will help continue you toward your fitness goals and the variety ensures it doesn't get boring.  It's a bummer about your 5k - but could you run/walk it anyway?  The last 5k I did (ok the only one I've done, I was trying to sound like an old pro!) only about 40% of the people ran it anyway.  Everyone else walked it. 

So use this month to turn yourself into a fish.  See Uttriman's winter logs if you need swimming motivation.  That guy grew gills.

I don't know about gill's, but I certainly got waterlogged (still am getting waterlogged for that matter!)

That said, get that knee some rest.  Don't push it so hard you do damage that will take forever to heal.  I tried that when training for a marathon once.  Ended up being sidelined from running for 16 plus weeks, because I couldn't run more than a mile without pain in the ankle (my sore spot).  I hadn't entered the world of triathlon yet.  Wish I had been because then I wouldn't have had to get all that endurance back.

Cross train, do non-impact workouts, and if necessary -- SEE THE SPORTS MEDICINE professional!  Don't play around with injury.  The risk is TOO high, even for the casual athlete!

i was talking to my PT today about this very issue.  He was saying that in reality you need a solid year of base training where you very gradually increase your mileage to allow your ligaments and connective tissue time to adapt to the new demands.  He said all injuries, besides those caused by major pronation problems, are caused by pushing your intensity and mileage faster then your connective tissue can adapt.  Unfortunately, none of us take a full year to ease into training and we usually push the envelope right off the bat, so we fight with injuries like this.

so ice ice ice and let yourself heal before pushing further.