What Michael said. There are another couple of ways you can achieve
the desired result:
1. Type the date in Word, and insert a non-breaking space with Ctrl-
Shift-Space. Copy and paste into PowerPoint.
2. Use Insert | Symbol. On PowerPoint 2007, the non-breaking space is
in Basic Latin right after the tilde (~).
<rant>
IMO, this is an annoying limitation in PowerPoint. Why they didn't add
the Ctrl-Shift-Space keystroke I don't know, since it does nothing in
2003/2007. My annoyance stems from the fact that the name of my
country (New Zealand) routinely requires a non-breaking space to avoid
being split across two lines.