You can. In fact, it's pretty easy.
You have to boot your PC with ghost for linux :
You create an image, on a USB disk, a second partition, a network drive, a ftp, whatever...
You create a vmware disk image, adjusting the size of the original disk/partition. You can create a bigger disk if you want.
You boot this vmware with g4l, and you deploy the image on it.
I did this once and it worked perfectly.
Of course, you may have to reinstall bootloader, maybe recompile your kernel, if you have a custom one (of course, if you are smart, you kept the standard one ;^) ).
An experimental trick can be the use of dd, or cpio from the mounted Slack partition to a "vmware-mount.pl mounted" disk image.
Rereading, i see that you are new to Linux, i hope my explanations aren't too obscure !!!
Post again if you have troubles !