assuming you are booting using lilo and not grub:
open /etc/lilo.conf in an editor and at the end add lines that say:
then exit and run "lilo -t" assuming it doesn't complain run "lilo" and when you reboot you should have the windows option added. btw, i assume your windows parittion is just the first one on the driver, if not you will need to change hda1 to a different parameter. run fdisk -l /dev/hda for a list.