If you're dual booting with Win2K/XP Pro (don't know about XP Home)... You might want to try this:
1) Install Lilo on your Slack partition (don't laugh yet, read on...)
2) Get BootPart from http://www.winimage.com/bootpart.htm
3) Use bootpart to create a boot image for your Slack partition.
Bootpart is nice for multi-booting, it's works perfectly on my tri-boot box (XP Pro, Slack, and NetBSD).