Everton Blair over at connectedinternet.co.uk wrote a nice beginners guide on how to increase the speed of your windows xp operating system.
The tips are all great ones that I myself use on my windows xp system. Tips include general ones that you´ve read on many sites like disabling indexing service but also advanced ones that beginners should not know about. Those include disabling performance counters, running Bootvis for faster boot times and removing fonts that the user and windows are not using.
He could have added more detail to some of the tips but a google search or a comment will help you receive the answer to your question(s).

The complete guide to optimizing Windows XP
Windows Boot Timer