I recently ran out of space on my virtual disk. I had over 60 gigs available in Mac OS X itself but my virtual disk was only 3gb. To expand the size of my virtual disk, I used the cli utility vmware-vdiskmanager.
Here's the command I ran on my Mac to expand the virtual disk.
"/Library/Application Support/VMware Fusion/vmware-vdiskmanager" -x 10Gb /Users/myuser/Documents/Virtual\ Machines/xp/xp.vmdk"