There are a couple of places programs get started from.
1.) the registry - you can disable these via the startup tab of MSCONFIG (go to START - RUN - then type MSCONFIG)
2.) The start menu - START - PROGRAMS - STARTUP (delete stuff in here by right clicking and choosing delete)
To find out if a program needs to run or not (and for more detailed explanations of how to remove stuff) check out the site below.