theakstonium,
You seem to be a little confused between programs INSTALED on your computer and programs that STARTUP when your PC starts.
When you install a program on your PC (a game, a word processor etc) they do not normaly autostart. They only start up when you select them to start.
Some programs do autostart, but these are generally very small programs that should not slow your PC down.
There is a useful program called WinPatrol that will list all the programs that autostart and you can look through the list and change them so they DONT autostart.
You can download WinPatrol for free from here
http://www.winpatrol.com/