I agree with Will. ERUNT is the way to go. Beats System Restore, IMHO.
NTREGOPT NT Registry Optimizer
ERUNT The Emergency Recovery Utility NT
http://home.t-online.de/home/lars.hederer/erunt/
ERUNT [[Note: The "Export registry" function in Regedit is USELESS (!) to
make
a complete backup of the registry. Neither does it export the whole
registry (for example, no information from the "SECURITY" hive is
saved), nor can the exported file be used later to replace the current
registry with the old one. Instead, if you re-import the file, it is
merged with the current registry, leaving you with an absolute mess of
old and new registry keys.]]
http://home.t-online.de/home/lars.hederer/erunt/erunt.txt
NTREGOPT [[Similar to Windows 9x/Me, the registry files in an NT-based
system
can become fragmented over time, occupying more space on your hard
disk than necessary and decreasing overall performance. You should
use the NTREGOPT utility regularly, but especially after installing
or uninstalling a program, to minimize the size of the registry files
and optimize registry access.
The program works by recreating each registry hive "from scratch",
thus removing any slack space that may be left from previously
modified or deleted keys.]]