In this helpful how to KB from our very own Doug Iman, he decribes at great length what is required to set up dynamic boot partition mirroring on GUID partition table (GPT) disks in Windows Server 2008.

This will be increasing helpful in the future as GPT begins to replace the aging Master Boot Record (MBR). While GPT disks technically still have some level of backwards compatibility by maintaining the MBR in the very first sectors of disk, this is mainly for disk utilities and other applications. Because of various differences between these types of disks, the steps required to enable partition mirroring have changed significantly.

For the complete guide see the following KB article, 951985: http://support.microsoft.com/?kbid=951985. If you'd like to know more about GPT disks, check out the above link to Wikipedia, or the Windows and GPT informational pages here, here, and here.

Any other questions feel free to leave a comment on this post.
Cheers,
Corey