PGP Whole Disc Encryption (i've been looking into it for work) v.9.5 is around $165 for a perpetual license, but you also want the universal server for key backups, etc. It's also fully compliant with imaging software and uses a single signon. It's steep, might be best to upgrade. I mean business oem with a volume key is what $100 per key plus medium?
As for BitLocker, I'm not exactly sure if it works with imaging, it should work with Sysprep. I mean this is Microsoft, one hand DOES talk to the other one, doesn't it? The problem is the needed hardware to run Vista properly, PGP doesn't need any upgrades and as I've been told, can run on just about anything.