I had problems here, I had Installed my slackware in External USB drive. During Setup process it can read the USB Hard Drive. But after installation Kernel panic appear. where slackware cannot mount my USB drive. Please someone help me.
How to make process that it read can read usb drive first than. everything gone be fine.
My Lilo were installed in master boot record (MBR)

My external USB drive IS 80GB Maxtor HDD.
Why during setup it can detect my External HDD? But not in my boot?

Because the usb drivers are not loaded until the kernel is loaded, lilo cannot find the kernel. Using an initrd (initial ram drive) in the boot process can help - this is done often to load scsi drivers for scsi harddrives. The use of boot and root disk that load the usb drivers prior to loading the kernel could also be a solution. The later can be accomplished for booting your current install by creating the needed boot and root disks from the slackware CD's. These disks can be created easily from within windows. The howto's are in the respective folders on the discs.

HTH