There is no good fix for this.
See
http://groups.google.com/groups?as_q=y+axis+truncated&num=10&scoring=r&hl=en&as_
epq=&as_oq=&as_eq=&as_ugroup=&as_usubject=&as_uauthors=&lr=&as_drrb=q&as_qdr=&as
_mind=1&as_minm=1&as_miny=1981&as_maxd=18&as_maxm=10&as_maxy=2006&safe=off
or, here's a shorter link:
http://tinyurl.com/yl9ofq
(the fixes are the same in PPT as in Excel)

Signature
Echo [MS PPT MVP] http://www.echosvoice.com
What's new in PPT 2007? http://www.echosvoice.com/2007.htm
Fixing PowerPoint Annoyances http://www.oreilly.com/catalog/powerpointannoy/
> How do I stop the Y axis title from truncating when I am working on a
> chart
> in PowerPoint?