Hi Preetha,
You can backup all the services by backing the below key from regedit .. HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services
Then go to c:\windows\system32\Group Policies and copy the three folders and place them on a pen drive or another safe place.
When you rebuild your system just double click on the system.reg to merge it, then open GPEdit.msc (the directory Group Policies isn't made until you run GPEdit.msc the first time, making the directory didn't work when I was experimenting with this) change one GP and exit then copy them from your pen drive or safe place.
Setup you desktop, restart, and done.
And hope you are aware that the services.reg is system specific? Using a exported reg file from one system on another will have unforseen consiquences.
Regards,
Prithviraj.