There is tool out that will create your VHD file in seconds. It is called VHD tool and does that job quite nicely.
Security is little bit compromised by using it since it does not fill that file with zeroes but it merely allocates space (that's where speed comes from). Because of that, data on your parent disk will be visible inside of virtualized environment.
I would tend to avoid it in production environment but for testing it surelly makes sence.