A good way to knock this on the head is to run the MSconfig function:
''Most people know that the more programs you have running on your computer at once, the more likely it is that your computer will either run slowly or even crash. What most people don't know is that every time you boot your computer a whole mess of "hidden" programs load in the background. Some of these hidden programs are essential, but most aren't. Turning off some of these hidden programs can significantly increase your computer's performance and reliability.''
http://netsquirrel.com/msconfig/index.html
Just be aware that theres all sorts of snake oil answers, load this, load that etc, but this is the most basic and effective way of stopping unwanted programs.