Read the readme that comes with zipslack it addresses this issue.
You need to go into the loadlin file and change the root=/dev/sda to root=/dev/hda
This is well documented in the readme
Reason for this before you ask is because zip slack was designed to be put on a zip drive not a harddrive nativly. But i must admit it makes one hell of a small base system. Only 100mb
by the way zipslack makes some strange lookin files when you read the fat file system in windows. This is because of the limitation on file names that the fat file system suffers.