There are four places that programs can put themselves to start when someone logs on:
In the Start menu, Startup programs. There are two places: "All Users" and the currently logged on user. Right click on startup programs and choose Open or Open All Users.
In the registry, two possible places:
HKLM\Software\Microsoft\Windows\CurrentVersion\Run
HKCU\Software\Microsoft\Windows\CurrentVersion\Run
Note that each user has individual settings in the HKCU hive of the registry and the user's startup programs folder.