I don't think so. I just tried last year's PowerPoint Live CD, which has
embedded fonts. I tried to open it and got the message saying that it could
only be opened Read Only. Leaving PowerPoint 2003 open, I switched to Windows
Explorer and installed the fonts. Returned to PowerPoint 2003 and it happily
opened the presentation file and allowed me to edit it.
I think one possibility might be that it isn't always easy to exactly match the
font. The above presentation uses Eras, but not all Eras font files are equal.
It actually uses Eras Bd BT, Eras Demi ITC, and Eras Ult BT. If I uninstall
Eras Ult BT (PowerPoint 2003 is still open) and then try to open the
presentation, it will only open as read only. So all embedded fonts have to be
identified and installed for it to work, and a perfect match is required.
The other thing that might be confusing is that if you search for installed
fonts in PowerPoint 2003 *and* you have a presentation open that has embedded
fonts, you'll find the fonts and there is no way to detect that they are only
installed temporarily. You have to close the presentation and create a new
blank presentation to do a reliable search in PowerPoint. So it's best to use
Windows Explorer and check C:\WINDOWS\Fonts to see the fonts that are
permanently installed. (I know you know all of this, but others might not.)