U May Have A Virus On Your Computer (Spy Ware,Add Ware). Which Is Slowing Down Ur Connection Speed. One Way To Tell This Is To Run Checks Through Ur Computer.
As LinoJennings says, you may have a virus. The best thing to use to check for these is ad-aware. You can download it for free just run a check every so often and you will be very suprised what at the amount of data miners etc. in you computer. This is the address to download ad-aware. http://www.download.com/3000-2144-10045910.html?part=69274&s ubj=dlpage&tag=button
Check the basics first,what speed is your modem connecting at assuming you are on dial-up. Hover your mouse pointer over the connection icon on your task bar to check this.Do not expect it to be a full 52k but anything substantially below this could even indicate a `dirty' or faulty telephone line. Even connecting via an extension can slow things down.