This hint certainly is obvious for some, but i didn't think of it at first. If printing from PowerPoint is painfully slow, try changing the background into white (or any other color) if a background picture or a fill effect is used.
This can be done either by Format -> Slide Background, or by eliminating the background picture from the master (assuming a master was used) under View -> Master -> Slide Master.
[robg adds: I thought PowerPoint had an option in its print setup to not print backgrounds, but that doesn't seem to be the case (perhaps it existed in the OS 9 version?). In any event, I can vouch for complex backgrounds taking nearly forever to print, even on fast printers. Disabling the background is a good solution to the problem -- however, if you've gone with a "light on dark" theme, you might have to change all of your text to dark, otherwise you'll get white on white, which is really hard to read!]
Mac OS X Hints
http://hints.macworld.com/article.php?story=2004011906203871