org-mode source blocks

[Hill]

I would like use the Source Code Blocks feature within org-mode. But I
found org-mode can't launch the language mode to edit the Source code.
1. Emacs -Q
2. M-x org-mode, then the emacs buffer entered the org-mode.
3. entering following test:
#+ srcname trait_demo.cpp
#+ begin_src c++
: using namespace std;
: int main( void )
: {
:   string tmp;
:   while(cin >> tmp)
:     {
:       cout << "from pipe: " << tmp << endl;
:     }
:
:
:   return 0;
: }
#+ end_src

4. C-c ' ;;then emacs lauch a buffer to edit the source code.
5. But the mode is "Picture" not c++ mode. Why?

I tried other language like python, it also launch a Picture-mode.
I would like to know. what's wrong?  My emacs version is 23.2.1 on
windows xp.

Any body can help? thanks!