1)

Kernel 2.4 may work better than 2.6, yes. But on the issue of connecting with an ATAPI Iomega Zip drive, I don't yet have any reason to believe a later 2.6 will work better than your 2.6.5.

2)

I see you say plscsi found your drive.

Now you can prove your disk is readable with a command like:

plscsi /dev/sg1 -i x200 -x "28 00 00:00:00:00 00 00:01 00" -t "" | hexdump -C

3)

I wonder if you understand, I meant for you to enter exactly: sudo plscsi /dev/sd[abcd]
That's bash shorthand for saying: sudo plscsi /dev/sda /dev/sdb /dev/sdc /dev/sdd

I think I see you say you can reach your Zip via: sudo plscsi /dev/sg1
but not via: sudo plscsi /dev/sd[abcd]

To my newbie eye, that's strange.

I wonder what you see at: lsmod | grep -i ide

I wonder if a bootline cheatcode that would help is: hdd=ide-cd