"Ippopotamo" is pronounced like this:
i - like the "y" in "happy"
pp - like the "pp" in "happy"
o - like the "o" in "orange"
p - like the "p" in "purple"
o - again like the "o" in "orange"
t - like the "t" in "trace"
a - quite like the "a" in "ask", just fully italian (I don't know how to explain that, it's the "a" of the International Phonetic Alphabet)
m - like the first "m" in "mum"
o - once more, like the "o" in "orange"
(specifically, it should be something like [ippo'pɔtamo] in IPA)