I misspoke earlier, the return value from ParseJSON is an roArray not an AA. So to look at the first item you just say "json[0]". The second is "json[1]", etc. Each of these items is an AA. The foreach statement will step through them. You can use PrintAA to examine the structure of each one: PrintAA(json[0]) etc.
You probably want something like
for each tweet in json
item.Message = tweet["text"] ' or tweet.text
item.UserName = tweet["user"]["name"] ' or tweet.user.name
BTW if you're unsure of what a variable is, it's handy to do "print type(var)" in the debugger.
--Mark