I think you need to rest it until the race. If you've done 10 miles already then your fitness is there so it is a case of rest until the race and get through it, keep training and not make the start line, or decide now not to run at all and look for another one to do later in the year (or next year) allowing you the time to properly treat it.
It does sound like the start of achilles tendonitis to me too. If you insist on doing the race, rest from running and other weight bearing exercise. Swim and cycling to maintain fitness as best you can in the next couple of weeks. Get some professioanl treatment on it - a physio or sports therapist should be able to help. Do lots of calf stretching (at least 5 times a day). I'm not sure about the eccentric exercising with the race so close. I known people who have started it and it has been worse for a couple of weeks to start with.
You need to attack it from all angles. Treating achilles tendonitis should consist of easing the pain and inflammation with rest, ice and anti-inflammatory meds.
You need to stretch the calf muscles, strengthen them with eccentric heel drops and get some massage and ultrasound.
But most importantly you need to work our why this happened. Usually it is overuse (too much hill work too soon) or biomechanical problems, or a combination of both. Get a lower body gait analysis (not just feet!) to identify any problems and correct with insoles/footwear/strengthening exercises
I agree with all the advice on glute strengthening for IT band syndrome. Make sure you are doing the side lying clam exercise (see video on above link). This is by far the best strengthening exercise for the gluteus medius.
As for if the half marathon is out of the question, it depends how far you were with your training and running distances before the knee pain. If you were already doing 8-10 mile runs then it shouldn't be too much of a problem. BUT if you had only managed 5-6, you might struggle. Also depends on if you are just doing it to finish or whether you have a target time in mind?
It all sounds like patellofemoral pain or anterior knee pain (same thing) to me. This causes pain anywhere around the kneecap and front of the knee. Typically aching and poorly localised, but can also cause sharper, shooting pains.
Is the pain/aching worse after exercise or the day after? Do you get any problems walking downhill or stairs? This is a common complaint.