Why don't you install LiLO in the MBR of /dev/sda. In that case your /etc/lilo.conf should look something like this:
# LILO configuration file
# generated by 'liloconfig'
# Start LILO global section
boot = /dev/sda
message = /boot/boot_message.txt
timeout = 1200
# Override dangerous defaults that rewrite the partition table:
# Normal VGA console
vga = normal
# End LILO global section
# Windows bootable partition config begins
other = /dev/sda1
label = Windows
table = /dev/sda
# Windows bootable partition config ends
# Linux bootable partition config begins
image = /boot/vmlinuz
root = /dev/sdb1
label = Linux
# Linux bootable partition config ends
After changing /etc/lilo.conf, issue as root "lilo -bvt /dev/sda" (b=specifies the Master Boot Record; v=increase verbosity; t=test)
If you get no errors there, then remove the t and issue as root "lilo -bvt /dev/sda" which will then install LiLO in the MBR of /dev/sda.
You will be booting Slackware from it's root partition, /dev/sdb1 and Windows from it's /dev/sda1 partition. I run 2 SATA drives in this box.
To boot with the CD at the boot prompt issue "sata.i root=/dev/sdb1 noinitrd ro"