good advice here, everybody's pretty much right on. it's true that different people respond differently to high altitude, and there's no good predictor of how any one particular person will do, other than past experience. what i mean is, what is your altitude history, particularly what is the highest altitude at which you've spent the night? if you've been to 14k before and had no problems, then odds are that you'll do fine up to 14k on huascaran. higher than that you can't really know until you try.
having said that, some will advocate a conservative ascent rate of no more than 300m a day, with a rest day every 1000m of total elevation gain, to prevent the onset of AMS(acute mountain sickness). this is probably too slow for a lot of parties, so the best thing to do is to listen to what your body is telling you. the earliest symptom of AMS is headache, others include nausea, vomiting, dizziness. if you begin to experience any of these during ascent, the best advice for you would be to look for the next available bivy site and spend at least one night out at that altitude in order to acclimatize. most people wake up the following morning feeling better and can resume vertical gain.
warning signs to watch for include confusion, incoordination, disorientation, stupor--all evidence of HACE(high altitude cerebral edema). HACE is ALWAYS preceded by AMS. other warning signs are persistent dry cough, coughing up bloody sputum, extreme shortness of breath--evidence of HAPE(high altitude pulmonary edema). if you have a healthcare professional on your team(always a good idea) they may hear fluid in your lungs when listening with a stethoscope. HAPE AND HACE REQUIRE DESCENT. further ascent in the face of either is NOT AN OPTION. both can be rapidly fatal, and likewise both can be easily treated--with descent. there are some medicines that can be given, like dexamethasone and nifedipine, but you should leave these up to the team physician, if you have one. another useful adjunct to descent in the treatment of HAPE/HACE is a portable pressure chamber, the most popular being the Gamow bag, but there's also one called the Certec bag which is a little lighter(10 lbs as opposed to 15 lbs). i have the address of the Gamow company in new york if anybody is interested.
about Diamox(acetazolamide): yes, it is a mild diuretic, but that's not really how it's useful in AMS. it's actually a carbonic anhydrase inhibitor, and to make a long story short, make your kidneys excrete(piss) out bicarbonate. this induces a mild metabolic acidosis in your system, which serves to stimulate your brain's respiratory drive. this prolongs the body's hypoxic ventilatory response and keeps your lungs working to oxygenate your blood. diamox can be taken prophylactically, though i personally don't advocate this unless you have a prior history of AMS. diamox contains sulfa, so DON'T TAKE IT if you are allergic to sulfa. and yes, it may give you tingling in the hands and feet and make you pee a little more. it will also make carbonated drinks taste flat(carbonic anhydrase inhibition).
DRINK LOTS OF FLUIDS. dehydration is more prevalent at high altiudes--your body loses lots of moisture in the form of insensate losses, like in your breath, with perspiration, with diuresis. so DRINK. dehydrated bodies are more prone to AMS. so DRINK. not but water or electrolyte solutions(better).
hope this helps. it's also always a good idea to have along an expedition physician(or some kind of healthcare person with experience) on the team, whether he/she is a climber or not, cause lots of nasty things can happen overseas on a mountain....
good luck and good climbing!