Anything went wrong with registry will potentially wreak havoc on the system. So before doing anything with Windows registry, it is wise to back up the registry by using Windows backup tool (All programs – System Tools – Backup). So that, at any later point you can restore it by using the same tool, if anything went wrong.
Here is a free tool WinMend Registry Defrag for defragging and cleaning windows registry. It utilizes Microsoft’s latest base level reconstruction technology that guarantees the maximum safety of your Windows operating system once the registry is rebuilt.
It can rebuild registry index safely and clear waste registry space to make it easy for Windows and other applications to find data more efficiently. As Windows registry is re-organized, you will enjoy much improved operating system performance.
This wizard interfaced program is very easy to use and support Windows 2000/XP/Vista (32-bit and 64-bit) operating systems. You can download the application from here.
For cleaning obsolete entries from registry you can always choose Ccleaner