Well, Slack comes with LILO, which installs by simply typing lilo at the prompt. However, before installing it you have to configure it, which is done through liloconfig (just type liloconfig at the prompt). You can set it up in different ways, the simplest being "automatic install", where it will (DOH!) try to configure LILO automatically - all you really have to do is choose where you want LILO installed (installing to the MBR is probably the most common). If the automatic install doesn't work, you can use the "expert mode", where you manually enter the location(s) of the partition(s) to boot. Since you dual boot, you'll have to enter the Windows partition (should be /dev/hda1) and your Linux partition.