If you are attempting to dual boot Microsoft and Linux, you need to re-size your partition first, but you didn't say that. I will assume you are going to run Linux only on it.
I'm not familiar with slack, but if I have ever had a Microsoft filesystem on a hard drive, I wipe it clean first by zeroing out the drive.
If you can get to a bash shell prompt, zero out the drive. I'm not familiar with laptops either, so I will assume that the drives are connected ide1 and 2, master and slaves as a tower.
Assuming one drive on ide1 master is your drive, give this command:
dd if=/dev/zero of=/dev/hda
This will write zeros on the drive, removing mbr and all, giving you a clean, unformatted drive, just as it would have come out of the box.
If you can't boot to a prompt, one of these should allow you to.
KNOPPIX Linux Live CD
Tom's Root and Boot floppy