Genuine SB 16 card? I haven't seen one in years, good cards for their
day though. Surprised you could find one, what kind of card did you
have before?

> At first I thought all was well, I can play mp3s using the card with
> no problems.

> That is until I start much of anything else (Firefox is the most
> troublesome). If I've got sound playing the machine freezes solid,
> ctral-alt-f1 and ctrl-alt-backspace do nothing. I can't ssh to it over
> the network. It's gone, and a hardware restart is the only thing that
> gets it up again.

This could be a resource issue, Firefox 3 is pretty resource intensive
for an older system, how much RAM does it have? Do you get any error
messages or does it just stop? And is it ONLY firefox or is it any
app while you are playing via the sound card?

> Some more Googling told me that this was a known problem back in the
> '90s, and that the solution was to not use full duplex mode and 16 bit
> sound at the same time.

Try disabling sounds from the OS, like Ubuntu has (like other OS's)
sounds for logging in, logging off, oepning/closing apps, etc... Go
into your sound properties and make sure it isn't playing any sounds.
It isn't the best solution, but then all you have to worry about is
sounds from a web site, since Ubuntu won't be popping off with any
sounds.

> Great, but I couldn't find any information that seemed the least
> relevant to modern systems telling me *how* to do this.
>
> I'll probably eventually figure it out, but I'm hoping that someone
> here already knows how to do this.

I'm not entirely sure how to configure it to half duplex operation,
might have to dig into kernel options...

lkml.indiana.edu/.../0743.html

That should give you a few clues, I believe (correct me if I'm wrong?)
the kernel options go into your boot line in GRUB. But test it first,
get to your GRUB menu at boot and then select the boot option you'll
be using and edit it, this won't be a permanent edit, then you can add
to the line that defines the kernel (at the end) sb16=blah,blah,blah

That should tell the kernel to load sb16 with those options.

If it works you can edit your /boot/grub/menu.lst file to make them
stick at every boot. After doing this, watch for kernel updates
you'll have to change its default (also in the same file) or change it
back to what you want after every kernel update.