What type of printer do you use? Some printers may require the driver to send
completely rasterized data at the final print resolution. If the printer runs
at hig DPI settings, that can add up to a LOT of data. For example:
720dpi X 720dpi X 3 bytes per pixel = >1.5mb
That's per square *inch* of paper.
Changing the printer settings (ie, from Fine or Photo to a lower rez mode) might
help.
It might be worth changing the Print Processor setting from RAW to EMF to see if
that helps (Start, Settings, Printers, Properties page for your printer,
Advanced tab, Print Processor button.)
If switching to a PostScript printer is a possibility, that'd be worth
investigating as well; PowerPoint's PS output is quite inefficient and porky,
to say the least, but it's still likely to result in much smaller spool files
than what you're getting. If nothing else, you can test it easily; install a
driver for a PS printer, connect it to FILE instead of to a port and print one
of these same presentations. If the file's notably smaller, you have a possible
answer.