Warning:Event Log and Remote Procedure Call (RPC) should never be changed regardless of what guides say. Most of the services are dependent on either Event Log and/or RPC so disabling these will cause almost every service to fail.
However, there are a few good sites that can help you through this:
3D Spotlight Windows XP Services Tweak Guide
Windows XP Service Configurations Note - site currently unavailable - May, 2005
Elder Geek - Services Guide for Windows XP
You may also notice in msconfig or the Task Manager that there are many other programs running besides the typical Windows services. For a great in depth explanation, check out the Pacs Portal page.
Keep track of your changes in the event you lose some functionality while tweaking your Services and Startup Programs. When in doubt, you can always refer to the link below for a list of the "Default settings for services" in a typical installation:
Default settings for services