First we'll look at Start -> Programs -> Startup folder.
Any programs listed there will run during Windows startup. Feel free to add/remove programs from this folder.
However many programs do not utilize this folder and you'll have to follow the steps below:
1) Start -> Run. Type in 'msconfig' and press Enter.
2) System Configuration window will be opened. Click on 'Startup' tab and you'll see a list of all programs that run during Windows startup.
3) Uncheck any programs if you wish to remove from startup.