The Windows registry on your PC is a set of files which store all the
essential settings for hardware, the operating system, the control
panel, application software, user preferences and user profiles, and
file associations (which programs run which types of files).
How is Windows XP registry repair done, and why does the Windows
registry ever need to be repaired anyway? At the bottom of this
article, there is a link to a resource page which gives access to
software tools you can use to repair the registry.
Repairing or cleaning the registry can also be done manually, using
the program regedit.exe (Registry Editor), which comes with Windows
XP, or with reg.exe from the command line. Manual editing is not
recommended though, even if you do a backup, because the registry
files are absolutely essential for the Windows operating system to
run, and it is all too easy to damage them by careless editing.
Microsoft Support itself says this - 'Although you can use Registry
Editor to inspect and modify the registry, doing so is not
recommended, as making incorrect changes can damage your system.'...

Registry Repair: http://groups.google.com/group/regrepairsbv