If memory serves i believe zipslack is a version of slackware that you can kinda install on top of windows, no repartition required, I dont really know a lot about it but i would suggest checking slackwares site (http://www.slackware.com)
If you are serious about getting into linux though I would suggest going with a different distro, one that you cant just throw on a fat 32 drive - Mandrake or Red Hat are in my opinion the best for newbies - you will need to partition or get a new HD, but its worth it in the long run
