You should be able to encrypt the entire image by installing the Encrpytion Desktop software onto the VM guest and setting it to encrypt the "local" disks.
http://www.symantec.com/docs/TECH149543
"Note: Beginning with version 10 of Symantec Encryption Desktop (formerly known as PGP Desktop), Drive Encryption is supported on server hardware including the following: Windows Server 2003 SP2 (32-bit and 64-bit editions), Windows Server 2008 SP1 & SP2, Windows Server 2008 R2 (64-bit), and VMWare ESXi4 (supported Microsoft Windows Servers operating in a virtual environment) Drive Encryption is supported on systems with internal hardware RAID-1 and RAID-5. Software RAID is not supported."