Thank you very much for your help.

This is my C++ code:

IStorage * pStorage = NULL;
hr = StgCreateDocfile(L"tmp.html",
                                  STGM_CREATE | STGM_READWRITE | STGM_DIRECT 
| STGM_SHARE_EXCLUSIVE,
                                  0,
                                  &pStorage);
if (FAILED(hr)) return S_FALSE;

IStream * pStream = NULL;
hr = pStorage->CreateStream(L"",
                                        STGM_CREATE | STGM_READWRITE | 
STGM_DIRECT | STGM_SHARE_EXCLUSIVE,
                                        0,
                                        0,
                                        &pStream);
if (FAILED(hr)) return S_FALSE;

hr = spMSXML->transformNodeToObject(spStylesheet, pStream);
if (FAILED(hr)) return S_FALSE;

Well, now the problem is that right after StgCreateDocfile() is being 
called, "tmp.html" file is created with length of 16K (16384 bytes). After 
transformNodeToObject() executes, my HTML is written into tmp.html, but 
_NOT_ _FROM_ _THE_ _BEGINNING_ of the tmp.html file. :( My output HTML in 
tmp.html starts in location 16K - myHtmlLength and ends at the end of the 
file. :(

What is going on?