Have 2 working VMs (e.g. culbor1 and culbor2)

Create a new disk for culbor1 with the following options: scsi, single-file, pre-allocated
Add the disk to the second VM (culbor2).
Open the .vmx-file for both VMs and change or add the following lines:

scsi1.present = "TRUE"
scsi1:0.present = "TRUE"
scsi1:0.fileName = "/VM/shared_disks/shared_disk.vmdk"
scsi1:0.redo = ""
scsi1:0.mode = "independent-persistent"
scsi1:0.shared = "TRUE"
scsi1.sharedBus = "virtual"
scsi1.virtualDev = "lsilogic"
disk.locking = "FALSE"
diskLib.dataCacheMaxSize = "0"

Make sure that you don't have any parameters twice, since it will result in an error when starting the VM.
This is assuming that you only have one hdd other than the shared disk attached to the VM. If you are using more then one hdd, change parameters accordingly.