We have adapted this information from an important series of tips from Tony Northrup at Microsoft:
You can examine autostart programs is to use the Autoruns freeware tool from the Sysinternals site. The Autoruns.exe program lists every program that will automatically start and allows you to quickly delete the link to the program. Many autostart entries are important parts of Windows XP, including Userinit.exe and Explorer.exe.
So you should not simply delete everything that you don't recognize. Instead, you can look up each entry at Paul Collins' Startup Applications List to determine whether you want it to start automatically. (I credit: Tony Northrup of Microsoft from this site for this important information. See the site for a lot of other tips on how to speed up Windows.)