PHP decode nested JSON

I've a nested JSON code as (it's actually my facebook status updates)

{
   "data": [
      {
         "id": "1290561400000000",
         "from": {
            "name": "My name",
            "id": "500920000"
         },
         "message": "Message body",
         "updated_time": "2010-08-24T08:22:13+0000",
         "comments": {
            "data": [
               {
                  "id": "129056140474641_8000",
                  "from": {
                     "name": "name1",
                     "id": "100000486072000"
                  },
                  "message": "hahahahahahha..........",
                  "created_time": "2010-08-24T08:40:39+0000"
               },
               {
                  "id": "129056140474641_8000000",
                  "from": {
                     "name": "name2",
                     "id": "1597542457"
                  },
                  "message": "true ya. I have updated",
                  "created_time": "2010-08-24T08:59:53+0000"
               },
               {
                  "id": "129056140474641_83000",
                  "from": {
                     "name": "Name3",
                     "id": "1000004860700000"
                  },
                  "message": "am putting it on my wall....",
                  "created_time": "2010-08-24T09:01:25+0000"
               }
            ],

         }
      }
]

Now how do I access the comments for a particular update and print it through a loop?? (I'm retrieving say a couple of updates at the same time).