I have tried to get ttyS1 on a Linux box to be a terminal. To the port I connected a second linux box with a serial cablepair/null modem setup and have minicom running. On the first linux box I did the following:

To the file /boot/grub/menu/menu.lst

1) Added to the kernel line "console=ttyS1,9600"

kernel (hd0,1)/boot/vmlinuz root=/dev/hda2 vga=0x317 selinux=0 splash=silent resume=/dev/hda1 showopts console=ttyS1,9600

2) added the following two lines to the top of the file

serial --unit=1 --speed=9600
terminal --timeout=10 serial console

To the file /etc/inittab I added

s1:2345:respawn:/sbin/agetty -L ttyS1 9600 vt102

When I reboot I do get output to the minicom terminal on the second box and I get a login prompt as below but I cannot type into the terminal (its like view only):

...
...
...
Starting HAL daemon done
Master Resource Control: runlevel 5 has been reached
Skipped services in runlevel 5: nfs smbfs

Welcome to SuSE Linux 9.3 (i586) - Kernel 2.6.11.4-20a-default (ttyS1).

linux login:

upon further troubleshooting the problem turned out to be the length of the serial cables. Using shorter serial cables and the problem disappeared. Take the thread as a How-To setup serial terminal for Linux.