If you are using windows XP and tweaking services using registry edit then there are things you need to keep in mind. You want certain changes in your windows you Google it and find ways to do it that requires registry hacks. But you should be very cautious while making any changes to registry. Registry is like nervous system for your Windows, it's a database that keeps information regarding configurations of users, applications, hard wares and many more things.

If your registry gets corrupted in any way then it can result in several critical errors or even BSOD. You should try to change settings using Control Panel. If you are editing registry then it should be advised from trustable source otherwise you can end up in a big problem.

Backup registry
You should backup your registry before making any changes to it so that you can restore it in case of damage. Third party tools are available to backup your registry. But System Restore is best way to backup your registry in windows XP.

In order to go to System Restore you should logged on as the Administrator or a user that have Administrative privileges.
Start -> all Programs -> Accessories -> System Tools -> System Restore.

Create a restore point by giving it a name. Now you have a backup and can go for tweaking.