Mailing a letter?

My friend just gave me her address in Japan, but I am nervous about sending her a letter!

Can I write the address in English on the front, and Japanese on the back? I am also confused about some of the kanji used for sub-districts and districts and the like.

For example, what is the kanji for saying "Tokyo-to" or "(sub-district)-ku?" Would Japanese mailing personnel be able to read if I wrote it in English (romanji) or Hiragana?

If you are not comfortable writing in Japanese, write the address in English only. Japan Post is able to deal with English addresses.

東京都 whatever区
(toukyou to whatever Ku)

It's better to write in Romaji than all hiragana, which can actually be harder for Japanese people to decipher. Japan Post staff will not have trouble with letters addressed only in Romaji- they must receive millions of letters a day just like that.

Don't worry, write the address in English, your letter will get there ;-)

I have written to Japan, and received in Japan, dozens of letters with English-only addresses.
You can write them in the standard US order (name, street, town, zip) or in the Japanese order (zip, town, street, name); they both work, no problem. Just remember to write country names in the addresses, and print in big, easy-to-read letters.

e.g.
Tarou Yamada
1-1 Chuo
Naka-ku, Tokyo-to 164-0011
JAPAN