Thank you very much for bringing me on the right track! It was indeed the harddisk which was configured as scsi by vmware
I was doing the installation wrong. During setup I used the test26.s kernel, which supports scsi. But after the setup, I chose the wrong kernel image to use with slackware. So I was booting with the 2.4 kernel, which doesn't support scsi, and gives a kernel panic.
Again many thanks to you all! It works perfectly now.