If it's a SCSI drive, it's very doable. People have done it with Jaz
I hear, and there's no technical reason not to be able to do with with
a zip (despite what people say, it should be fast enough to be usable
for repair work, demoing, etc). But you'll probably never be able to
boot a parallel port zip on PC hardware, without bootstrapping from
something else (floppy, harddisk, or cd). Or you could write your own
BIOS :-)