Well, depending on what partition windows is on, it could vary (I'm assuming it's the first partition on the primary hard drive, hda1)
To add this follow these steps:
1. Open up Konsole
2. type in these commands:
su
(enter root password)
kwrite /etc/lilo.conf
After KWrite comes up, add this anywhere below the line "menu-scheme=wb:bw:wb:bw"
other=/dev/hda1
label="Windows"
table=/dev/hda
(only make sure there's a tab in front of "label" and "table")
If you want windows to be the default, edit the top line to say:
default="Windows"
Save and exit. Back to the shell, enter this command
lilo
and it will be fixed. The windows option should boot windows.
Note: If windows is not installed on /dev/hda1, it will be different. Open the mandrake linux control center, click on "Mount Points", and then on "Partitions". Click on the windows partition, and see what it says in the Details section. If it says something other than hda1 (hda2, etc) then change "/dev/hda1" to "/dev/..."
Let me know if this helps