I presented on this at TechEd Hong Kong. You can with Windows Deployment Services, deploy a BitLocker partitioned machine. The key is to create two partitions. One is for the un-encrypted boot (or as we call it the "System") portion and the rest is for the Vista (or Longhorn Server for that matter) OS Boot. The system partition needs to be 1.5GB at present, formatted and marked Active. The boot partition is then extended to the rest of the disk and formatted as NTFS also.
Heres how to setup the rest.
My Windows System Image Manager Script should help you get started. It partitions the disk up and then does a modify operation to format it and mark the partitions correctly. Make sure you change the logon parameters for WDS to reflect your installation else it will fail the install. In my script I have it partitioning a 2GB system partition and extending the rest of the disk. Change it as you need it.