Ho Mo it's hard to tell anyone what they should do without knowing your spec but if your computer is really slow maybe you should first check why before installing anything else. Belarc which can be downloaded gives you a complete run down of whats installed and your spec which you can copy and paste on here if you wish.
There's also a great FREE site that will find the obvious and tell you what you can do to improve performance if possible.
Using INTERNET EXPLORER go here
http://www.pcpitstop.com/
Click on Overdrive it's on the left
When the next page opens go to the bottom and click on
run OverDrive anonymously.
on the next page click
don't create an account
on the next page you will get a message this webpage wants to install the following add on.....it's 100% safe
click install
A box will open up do you want to instal this software click
install
That will take you back to a previous page again click
do not create an account
That will open up another page click
LETS GO
A box comes up click
OK then sit back and relax.............it takes only a few minutes with check your video card, your drives will advise you if you need to clean out junk box tell you if you should install more ram etc.
If it's not the lack of ram I might be able to put you on to a very good program that will look after most things on your comp and keep it running smoothly with no effort from yourself...it's not free but there are ways and means of making it free :0)
Don't be buying anything especially not Norton as the guys say it hoards memory and is a pain in the backside.
The best is ESET if you are going to buy a antivirus but there's no real need these days Microsoft is as good as any.
A good anti spyware is essential if you don't already have one........
http://www.safer-networking.org/dl/ Download Spybot 2 Free Edition malware and spyware are notorious for slowing down computers.