Okay so stupid question... Did you restart IIS after you changed the php.ini?
I took a look at your dropboxed php.ini and the extension= section it looks okay to me. PHP looks for php.ini's in a couple different places on windows. Can you make sure that there are no other copies lurking around by moving them some place where it won't look (aka outside the PATH or into the recycle bin). Then restart IIS and see if that helps.
Note: the reason I'm asking you to do this is two fold. 1. because if phpinfo isn't reporting an imap section then your either missing the php_imap.dll file , or there is another php.ini over writing the running one. 2. just to rule out the possibilities of multiple php.ini files.