If you are on Windows XP, ME, or 98 simply go to START>RUN>MSCONFIG then to the startup tab. There you can check or uncheck items that come up with windows.
You also might want to check out WinPatrol. Not only does it give you an in-depth look at startup programs, but it also monitors your system in real time and notifies you of startup changes among other things.
if u have enough knowladge about computer then u can directly modify the boot.ini file from u r system folder cause all the boot sequences are there inside boot.ini all the other application i mean third party applications changes this file to make changes if u r expert change it from that file