Bear in mind that as a default the virtual disks in VMware are SCSI types, connected to a "simulated" SCSI host adapter [at least in my old version -- not sure about version 5]. So it may be that the kernel used in the install system is not compiled with the correct scsi driver. I'm not sure about Slackware, but anyway you can try these:
1 - change the VMware config to emulate an IDE disk instead of a SCSI type (not recommended by VMware for performance reasons)
2 - in the slackware installation system see what scsi chipset is emulated by VMware (I used to know this by heart but I forget -- use "lspci" to find it out); then see if there is a module by trying "modprobe xxxx" where xxxx is the module used for that chipset (a quick google search).
Also, some floppy-based distros have an extra floppy containing scsi drivers -- this is all very dependent upon the distro (Fedora's kernel obviously had less trouble
Good luck with it!