Check for open Excel document in C++

I've recently updated our PCs to run Windows 7 32-bit from Windows XP. The code I had used in the past has stopped working and I was wondering what I could do to get it working again.

FileStr.Format("Microsoft Excel - %s  [Read-Only]", pathStr);
HWND hWnd= ::FindWindow(NULL,FileStr);
if (hWnd == NULL)
	ShellExecute(NULL, "open", pseMULTI.m_tProductionTaskfBriefPath, NULL, NULL, SW_SHOWNORMAL);

 
Obviously Windows have changed the way it window names, and I appreciate that the way I had been doing it was a complete fudge.
 
Any help appreciated.
 
Thanks.