Since no one answered my questions about serial lines, I went ahead
and bought a two port 16550A compatible card.  It looked to me,
from examining serial.c, like the driver supported IRQ sharing on
COM1 & COM3, and COM2 and COM4; however my attempt to do that failed
(locked up my serial mouse on COM1).

So now I have the first port on my card using IRQ5, and the second
port is disabled.  Can someone please tell me what the "right" way
is to get four serial ports?  Is there a way in Linux to find out
which IRQs are in use?

                Thanks in advance for any replies,

                        Eric Negaard