Although ADPREP executable exists on the Vista DVD (\sources\adprep\adprep.exe) with accompanying LDF files (sch14.ldf - sch39.ldf), you should NOT use it to extend the schema of Windows 2000/Server 2003/R2 Active Directory. These files are there for informational purposes only for showing what Longhorn Server will bring along when it'll arrive.
Windows Vista Bitlocker recovery keys cannot be stored in the Active Directory before extending the schema and modifying AD permissions. The information and tools to perform these preliminary tasks will become available some time in the near future - when it's ready, I guess ;) In the mean time, you could have a look on extending the schema for Vista wired and wireless group policy @ http://www.microsoft.com/technet/network/wifi/vista_ad_ext.mspx.