The Windows XP Optimization Guide

Step 5 Services

Services can be adjusted by going to start > Run > (type) services.msc. Services are components of the operating system that provide different features. Right Click the item, go to Properties > Startup Type: to modify the setting.

There are three different settings for each service - Disabled, Manual, and Automatic. Disabled means the service cannot run. Manual will run the service when needed, and Automatic will start the service whenever Windows starts. Do not disable unless you are certain the service is unnecessary and will not be run.

These settings are to be changed assuming that all your services are at default and you have SP2. If not, get SP2 first! These settings will apply the next time Windows starts up.

Modify the following to the indicated settings:
Distributed Link Tracking Client - M
Fast User Switching Compatibility - D
IMAPI CD-Burning COM Service - M
Indexing Service - D
Net Logon - D
NetMeeting Remote Desktop Sharing - D
Remote Registry - D
Secondary Logon - D

From TweakHound
Another good resource

Optimization Myths Is a good read, however, deleting certain services does indeed speed bootup time.