A as in "Caught"
I as in "Tea"
U as in "Who"
E as in "Egg"
O as in "Oh my gosh"

Example: Karate = Kah Rah Tay not Karotee
                 Karaoke = kah rah oh kay not Karyokee

You will also notice almost all Japanese words end in a vowel sound with the exception of words ending in "N". In cases were the word ends in "U" the U is practically silent. Example "Desu" would sound like "Dess"

R's and L's are also considered the same sound. Pronouncing these is like rolling your "R"s only 1 time. It comes out sounding almost like a "D" like when you say "Murder".