I appreciate what everyone's said about Norton - it does slow a PC down. But if you want to stick with it for the time being, I'll give you another option to try.
Try deleting as much as junk as possible from your PC by following the instructions here:
http://www.helpwithwindows.com/WindowsXP/howto -16.html
You will need to be able to view hidden files and folders in order to carry out some of the steps. Instructions for this are available on the web.
After you've followed the instructions, defragment your hard drive by either using the disk defragmentor in Windows (assuming you have XP) or a free one from the web. Here's a good one:
http://www.download.com/Auslogics-Disk-Defrag/ 3000-2086-10567503.html?part=dl-Auslogics&subj =dl&tag=button
After you've done all this, you will almost certainly find an increase in your connection speed. Whilst I accept that the ISP is often responsible for the slowness of a connection, you can help the matter yourself to some extent.