Same source file, two formats, three filenames.
Definitive answer? Wordpad on Vista does not open Word .DOC files.
Left to right: .DOC, RTF, RTF with .DOC extension.
[image|http://homepage.ntlworld.com/peter.whysall1/vista_wordpad.png||||]
Just to prove the point (notice how the .DOC version is wrapped differently to the RTF version):
[image|http://homepage.ntlworld.com/peter.whysall1/xp_wordpad.png||||]