If you are using Windows XP, It is possible to increase your internet speed by %20. Windows itself uses %20 of your bandwidth for updating and scanning your pc. By turning this feature off, you can gain %20 of speed. Here is how to do that:
1. Go to Start-> Run-> and type gpedit.msc
2. Expand the Administrative Templates branch
3. Expand the Network tab
4. Highlight QoS Packet Scheduler
5. Click on Limit Reservable Bandwidth and check the enabled box
6. Then Change the Bandwidth limit % to 0 %
Then restart your computer and you will see the difference in speed of your internet.