In addition to reducing the number of programs which run at startup. several methods as how to accomplish that task having already been suggested, I believe you should also consider disabling those services, which also run at startup, that you do not need.
Go to START/MY COMPUTER. right click and select MANAGE. The COMPUTER MANAGEMENT window will appear. Select and click on SERVICES. Scroll through the services, and by individually highlighting each one, information concerning the service is provided. By right-clicking a service and selecting PROPERTIES, you can set the service to operate manually or automatically, or to disable the service.
As a general rule, services that you need to always run should be set to automatic, services that you want to be available to run should other programs need them should be set to manual. and services that you don't need should be disabled. Remember, however, that a service may depend upon another service(s), so you must learn those interrelationships by reviewing the available information.
The following web sites should provide the information you need to make the proper decisions:http://www.theeldergeek.com/services_guide.htmhttp://www.ss64.com/ntsyntax/services.htmlhttp://www.z123.org/techsupport/xpservices.htmhttp://www.overclockersclub.com/guides/win..._services_2.php
The reduction of startup programs and services will help free up resources. If you are still not satisfied with your computer's performance, you should consider additional RAM, assuming you have room for expansion. It is one of the lowest cost ways to increase resource availability.