As far as I know you used to be able to access those files prior to Service Pack 1. SP1 applied a fix so that those files became inaccessible. Have you tried accessing them through dos?
c:\> reg query "HKLM\System\CurrentControlSet\Control\BackupRestore
\FilesNotToBackup" /v "System Restore"
And then, you can cd to the System Restore Directory.
(example)
c:\> cd \System Volume Information\_restore{8716531F-212F-45F1-8BAA-
FB69F0C7FAEF}
Within Restore Point Directories(RP0, RP1, ...), you will find a
directory called "snapshot" including registry hive data.
_REGISTRY_MACHINE_SAM
_REGISTRY_MACHINE_SECURITY
_REGISTRY_MACHINE_SOFTWARE
_REGISTRY_MACHINE_SYSTEM
_REGISTRY_USER_.DEFAULT
_REGISTRY_USER_NTUSER_S-1-5-18
Haven't tried it but I don't think it will work anymore...
.....