vmware-vdiskmanager -x 10GB your_virtual_disk_name.vmdk
How easy is that. 10GB is the end size you want to have. For example if you have HDD which is 10BG and you want to increase it to 20GB you have to use the following command:
vmware-vdiskmanager -x 20GB "your_virtual_disk_name".vmdk
After that start your VM and log in. You need to format the extended HDD. For example, if you use WIN2003 you can see that there is 10GB unformatted unused space which you can assign to a new disk.