Your best bet for hdd to vmdk conversion, i.e. transformation of VirtualBox disk image (.hdd file) to its Vmware counterpart (.vmdk file), is to use the the standalone VMWare vCenter Converter. A viable alternative would be some virtualization software with support for both of these formats; VirtualBox should do apparently.
Open HDD file Open VMDK fileFree system virtualization platform for Linux operating system developed by Oracle