Have you considered boot from SAN? Windows 200 and 2003 support it, so it is really just a matter of finding a SAN vendor that supports it at the hardware level.

Boot from SAN in Windows Server 2003 and Windows 2000 Server

http://www.microsoft.com/windowsserversystem/wss2003/techinfo/plandeploy/bootfromsaninwindows.mspx