I currently use PowerPoint on PC (v 4.0a)
I don't meet such a problem too.
1 - double clic on the graphic to enter GRAPH procedure
2 - select the Y axis title
3 - press right button to get the menu
4 - choose 'format of axis title' option
5 - In 'alignement' chapter, choose the orientation you want to give
to the axis label
Excuse my approximative English !
Hope this will help
Regis Plichart
Institut de Recherches Medicales
PAPEETE - TAHITI
French Polynesia