http://bugs.winehq.org/show_bug.cgi?id=33333
--- Comment #1 from Rosanne DiMesio dimesio@earthlink.net 2013-04-04 12:27:53 CDT --- Powerpoint 2007 starts up fine on my system in 1.5.27 with the override for riched20.
Try reinstalling to a clean wineprefix, and set the override for riched20 before you attempt to run Powerpoint the first time. The prompt about safe mode on subsequent attempts is not a bug; Powerpoint is supposed to do that after a failed attempt to start.