The way you normally restore the registry from the last good boot is by using the "Last Known Good" option from the Recovery Environment.
Have you tried running Chkdsk from the Recovery Environment?
I assume you copied the System Hive to the Windows\System32\Config folder.
You don't have any restore points, or a System Image Backup?
But if your system is experiencing continued corruption, you may need to take drastic steps to stop it. As bassfisher6522 mentions, sometimes it is best to just start over. Whether you do a complete reinstall, or if you have the SP1 Install DVD, perhaps a repair install.