look in /System/Library/LaunchAgents and /System/Library/LaunchDaemons folders, they are available both in / and user account folders, typically you'll find .plist files describing auto-starting apps there.
Click and hold on on of the icons on the dock that belongs to a program you don't want to start. Under options (may vary depending on your OS version) see if you can uncheck Open at Login. Let me know if it doesn't work!
look in /System/Library/LaunchAgents and /System/Library/LaunchDaemons folders, they are available both in / and user account folders, typically you'll find .plist files describing auto-starting apps there.