Scale the ASA rating of your film to the weather, tending towards faster film. If it's going to be outdoors and very sunny then use 100/200 ASA. If it's a bit grey or overcast use 400 ASA, if it's winter nasty, use 1000 ASA.
You shouldn't use flash, and it's probably banned anyway, so I'd recommend 400+ ASA to be on the safe side. T-Max 3200 B&W is great for the reptile house and indoor features.
If there's mesh or glass between you and the animal, switch to manual focus to avoid the auto-focus choosing the glass/mesh instead of the animal.
Chat to and befriend the zoo staff and ask them about how to get a good shot - some of them might like to have a copy of a picture in return for letting you round the back at feeding time. Find out feeding / cleaning time and ask the staff when the best opportunities will be - maybe phone the zoo before you go to ask about photography tips.
Good luck and post your results for us to have a look!
Rob