Resetting administrator password on Windows server 2008 R2 over Raid
I always use Windows Password Resetter to do stuff like this. It works well enough to blank the Adminstrator password (allowing you to reset it on next login). The bootable Live CD can usually see most drives I deal with (provided I am using real, bona-fide hardware RAID).
Haven't had to try it on Win7/2008R2 yet, though -- might be some restrictions built into those operating systems regarding logging in with blank passwords.