Windows Xp tries to be everything to everyone. It has many built-in services which take care of various functions of the operating system as well as give us more than enough to live with. The problem is, most of us don't need all these services most of the time. These services however utilize a lot of system resources slowing down our computer. For example: if your computer is not in a domain, various services relating to it can be disabled without harming your internet connection. The services can be accessed by going to Start> Run> type services.msc and press Enter. It can also be accessed by going to Start> Control Panel> Administrative Tools> Services.
There are some services like Alerter Service, Clipbook Service, Computer Browser, Help & Support, Indexing Service, Messenger, Net Logon Service, Remote Registry Service( should be disabled for security reasons), Smart Card, Universal Plug & Play Service, Workstation etc which can be happily disabled.
There are many more services apart from these which are most of the times unwanted. However, it is better to go through the description before making any changes to the services. It is always better to keep the default setting for the services which we do not understand. There are some services whose description cannot be understood by laymen. Therefore, it is better to leave them alone.