Okay, per your advice I downloaded Firebug and checked the POST data for checkout/shipping/quote:

Headers Data:
Request Headers
Host www.visionandhope.org
User-Agent Mozilla/5.0 (Windows; U; Windows NT 5.2; en-US; rv:1.8.1.14) Gecko/20080404 Firefox/2.0.0.14
Accept text/xml,application/xml,application/xhtml+xml,text/html;q=0.9,text/plain;q=0.8,image/png,*/*;q=0.5
Accept-Language en-us
Accept-Encoding gzip,deflate
Accept-Charset ISO-8859-1,utf-8;q=0.7,*;q=0.7
Keep-Alive 300
Connection close
Content-Type application/x-www-form-urlencoded
X-Requested-With XMLHttpRequest
Referer https://www.visionandhope.org/cart/checkout
Content-Length 629
Cookie SESScc755b1b98759a464bea40686f3e0085=b05b5c43eeaf4e0cf6f659c4e96e67af
Pragma no-cache
Cache-Control no-cache

Post Data:
details[address_select] 0
details[city] Los Angeles
details[company]
details[country] 840
details[first_name] Arash
details[last_name] Abcdef
details[phone]
details[postal_code] 90025
details[street1] 2025 Sawtelle Blvd
details[street2]
details[zone] 12
products 6%5EAK%5EAK1%5E%5E1%5E0%5E4%5E1%5Ea%3A4%3A%7Bs%3A10%3A%22attributes%22%3Ba%3A1%3A%7Bi%3A2%3Bs%3A1%3A%228%22%3B%7Ds%3A5%3A%22model%22%3Bb%3A0%3Bs%3A6%3A%22module%22%3Bs%3A10%3A%22uc_product%22%3Bs%3A9%3A%22shippable%22%3Bs%3A1%3A%221%22%3B%7D
uid 1

Response:
Loading...

Furthermore after some time I get a syntax error