If you have considered running Bitlocker, Microsoft's drive encryption tool, but didn't want to bother with what it would take to setup your drives properly to support it, then you are in luck if you are running Windows Vista Ultimate edition or Enterprise edition Microsoft has made a tool just for you. The Bitlocker Drive Preparation Tool is designed to help convert your existing install of Windows Vista into a setup that supports Bitlocker drive encryption.
Windows Vista Ultimate users can get this utility today as an ultimate extra from the Windows Update control panel applet and if you are a Windows Vista Enterprise customer you can head over the premier website and look under the tools section https://premier.microsoft.com/troubleshoot.aspx?taid=tools or contact Microsoft customer support.
This tool will automatically create an S: drive that is 1.5 GB in size and move over the required boot files. This new partition become the active partition that begins the boot process. It will not be encrypted, only the operating system volume will be, so don't store any data on this partition. The reason for such a large amount of space is to support WinRE and Microsoft updates.