If you can access the hard drive in question from your computer, I take it that the hard drive has not crashed, in which case there must be another solution, IMO. I suppose you already tried safe mode and restore and other boot options?
However, I do seem to recall that you can export and import registry files in regedit. If that is the case, then it may in fact be possible to access the registry in the manner you wish, if the folder (I assume the system folder) is accessible, which it may not be.
“In Windows XP, 2000, and 2003 there are several Registry files. These files are named without a file extension and are stored in the Windows\System32\Config folder. These files are named Software, System, SAM, Security, Default, and UserDiff. There is one more Registry file and it does have a file extension, NTuser.dat. In Windows XP, 2000 and 2003. NTuser.dat is stored in the users folder under the Documents and Settings folder. Each user has their own NTuser.dat file. The NTuser.dat file stores all settings that each user selects; these settings will override settings stored in the System file”
Whether or not regedit will open these files in this way, I can’t say. Frankly I will be surprised if you can access the system folder at all without booting the drive.
Good luck to you.