Does opening a program in your computer give you a tea break? Do you spend lots of time waiting for programs to open or close? If the answer is YES - then you need to better look under the hood (Same as what your mechanic does when you drive your car to him). A recent finding by a popular computer magazine came up with the list of software's that were the major cause for PC's to run slowly.
Have a look at the list below and make a choice when you are installing these. Look for alternatives in the web for light-weight programs that'll be as good as these or sometimes better. For example, the first on the list is Norton - I had sensed this a few years back and from that time I use AVG Anti-Virus on all my home machines - it has a free version for home use and consumes very less memory and best is that it doesn't slow down my PC.
Time to look under the hood and make the right decision.