Microsoft, in its wisdom, revised the serial port "interface" in its latest 2005 iteration. MSCOMM is no longer used. I can only speak from my experience in Visual Basic 2005, but it seems to me that both C and VB have been nudged closer together in the .NET approach that Microsoft has chosen.

I recently wrote an article on using the serial port in VB2005 in the Dec 2006 edition of Circuit Cellar, "Visual Basic 2005 and the Serial Port".

http://www.circuitcellar.com/magazine/197toc.htm
(CC charges a small amount for the download)

Although I can't promise, I suspect there will be a large degree of commonality between VB and C. In the help files of VB (and therefore I presume for C) there is a link to the Micrsoft forum and you will probably find reference to this subject already if you search. MS actually monitors the forum and sometimes answers as well as other fundi, so you may want to pose the question there.

Hope this is of some help
-Aubrey