Fanmail.biz

is it possible to send a letter from New Zealand all the way to USA and how would i do this?

wrong forum to ask this...but ofcourse it is possible why wouldn't it?
I send from Belgium to the USA too

Yes this is quite possible. Send the letter airmail and it will get there. For the return postage, you need to get the likely weight/size and check USPS for an online calculator. You will need to purchase sufficient International Reply Coupons (available at post offices, try the largest one near to you) for return postage. Each IRC has a value of US$0.98 so you can work this out with the USPS cost given as to how many you should send.