Have you ever taken a glance by the time in the lower right hand of your computer and notice a number of icons sitting there. When you install most programs, they have a small part of the program running, so when you finally need the program it doesn't have to start loading from scratch and it starts faster, another use is to automatically check for updates and specific intervals.
These are all legitimate uses, but when you start to install a number of programs and they all do this, it starts to slow the system down and it takes a bit longer to start. AOL, itunes, quicktime, AIM, Google Desktop are all culprits.
There is a quick and easy way to deal with this, if you are comfortable using computers hit start > run and they type msconfig in the dialog box and hit enter, then hit the startup tap. You will see a list of programs and a check box beside it to see which ones start with the computer. I usually remove them all except for my anti-virus and firewall programs. After you it ok it will ask you to restart. On your first restart a dialog box will open telling you that system changes have been made, check the box and hit ok.
If after making any changes, some of your programs don't work the same or if you need something to start with the computer such as a fax program or Magic Jack phone service, put all the check boxes back and disable them one by one.