I don't know of a better method than to list and identify each program, determining what it does and if it's required. Before that you had to start by right clicking every icon on the bottom right to see what it indicates is running and set it not to start with Windows if you don't need it, then checking the START list under STARTUP for others, then MSCONFIG and finally (very risky) editing the registry.

Never know what might be on a machine. Even without viruses and spyware there could be preloaded instanrt messaging or online service offers that run. Could be as simple as "printer services" where you do need one to print, but not the one that constantly estimates ink levels. If Microsoft Office is autostarting its much better to change that and just open if and when you need it. The possibilities really are endless so it comes down to make your list and check the items.

There are files called "Windows Services" that you don't want to change unless you are prepared to recover from a crash. Most are required for the machine to run and many are interdependant. These don't show up in task manager or task listing programs so while you can't accidently alter them, don't go searching for them either. If your willing to chance reloading Windows do a search for "Black Viper". But more likely, any significant problem will be easy to inentify and remedy without dismantling the operating system.

The startup list will have a lot of duplicates because programs will show in the "Running programs" section and the part showing how they start. So you can knock off two or three lines at a time. The two choices are let someone who's done it check yours, or do it yourself then use the experience to assist another.