Was your onboard serial port disabled in the BIOS at the time you installed Debian? If it was, then the first port on your serial card should be mapped to /dev/ttyS0. If not, then udev may have picked up the onboard port as /dev/ttyS0 and made your card /dev/ttyS1 (or another number).
No, originally the on-board serial device was enabled in the BIOS when I plopped the card in, I've since disabled it in the BIOS and sometimes now when I reboot this box, and run setserial, I will see either one or two serial devices listed. The on-board device always showed up with a low IRQ and the Serial card is IRQ16, so I was able to tell which device I was using. During my troubleshooting, before sending my initial email), I had set everything up to use ttyS0 and ttyS1 anyway, just to cover all my bases, but I still got no login when I tried to connect via serial.
I have two Debian 4 boxes with the serial console working. It has been quite a while since I set this up, but I'm pretty sure that I just added this line to /etc/inittab and then restarted init:
co:2345:respawn:/sbin/getty -L ttyS0 9600 vt102
I think the "co" may have something to do with it. Sorry I can't be more help, I'm really rusty on this. I did this 5 years ago and I've never had to do it again.
What does co do vs TO? Admittidly, I don't know much about how this works, so like a smart monkey, I did what I saw wrote about the most. Also, how are you restarting init w/o rebooting?
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> A: Yes.
> >Q: Are you sure?
> >>A: Because it reverses the logical flow of conversation.
> >>>Q: Why is top posting frowned upon?