my advice is to install slackware to ur 80 gb partition,
u can use the swap of linux mint.
and install lilo to the root partition of slacware.
i hope u r now using grub of the linux mint, for dual booting with xp,
then chainload the slackware entry in the grub of linux mint. (this is the easiest way and advantages are many)
then your menu.lst should have 3 main entries
1. corresponds to linux-mint
2. slackware- chainloaded
3. windows - chainloaded
i hope u r going to install fedora 13 on the same space. in that case please try with slackfore some time and configure it completely and then remove
if more help is needed, dont hesitate to ask
edt: chainload entries should have a form like this
where x has to be replaced by the corresponding partition number.