After a brief search of the usual haunts, I can't seem to find a
reference to this problem and would value confirmation of it's
existence on someone else's system, or directions to a URL of
relevance. My problem: the PPP system preference which should allow my
modem connection to remain active between logouts does not appear to be
working.

So you're saying that the "Disconnect when user logs out" in the PPP options window is *un*checked?

On my iMac 400 DVD, I am disconnected before logout is
completed, whilst on my Pismo 500, and this is more alarming, I get a
previously unseen error message (thoughtfully replicated in about 6
different languages) informing me that I must restart my computer
immediately. Any thoughts?

That message is a kernel panic, which is a bad sign.

Use the Console utility to check to see if there's anything obvious in there, or check out the file /Library/Logs/panic.log which should provide some info.

Thanks,
Shay
--
=========================== Shay Telfer ================================
Perth, Western Australia Technomancer It must be bunnies!
Opinions for hire [POQ]
[EMAIL PROTECTED] fnord