msconfig for windowsXp otherwise you can find it from Registry
look in [hkey blah blah] i.e. located in many of em in
Software\Microsoft\Windows\Current Version\Run & RunOnce open each one and you can see what's there
Other way that you can disable but not delete them using spybot search and destroy http://www.safer-networking.org/
in the advanced mode you can check for the running programs at startup also you can clean up your system from spywares too heh!
If you are using XP, or 9x, then click start / run / type msconfig
If you are using windows 2000, that command wasn't included, so look in your start menu, under Startup, and 2 places in your registry: (click start / run / type regedit