The following code example makes the existing "C:\MyFolder" directory a public file share. Later you can set passwords to that file share and also which users can access it. Below example is taken from MSDN, you can look around for more information with the ADSI interfaces. So the idea is keep in a NTFS folder and then set AD properties. Hope this helps...
IADsFileShare *pShare = NULL;
IADsContainer *pCont = NULL;
LPWSTR adsPath = L"WinNT://yourMachineName/LanmanServer";
HRESULT hr = S_OK;
hr = ADsGetObject(adsPath, IID_IADsContainer,(void**)&pCont);
if(FAILED(hr)) {goto Cleanup;}
hr = pCont->Create(CComBSTR("FileShare"), CComBSTR("Public"), (IDispatch**)&pShare);
if(FAILED(hr)) {goto Cleanup;}
hr = pShare->put_Path(CComBSTR("c:\\public"));
if(FAILED(hr)) {goto Cleanup;}
hr = pShare->SetInfo();
Cleanup:
if(pCont) pCont->Release();
if(pShare) pShare->Release();