Jerky Scrolling & Typing

I tried this under security but maybe it should have been here. I've check out several boards and seen problems close to mine but the fixes don't work. This started a couple months ago about the time I upgraded Netscape but I can't swear that has anything to do with it. I've always used Netscape because it runs faster for me. When I scroll it is either very slow or it stops for a few seconds and then jerks to catch up. Typing does the same thing. I will type several words before they all of a sudden show up on the screen. All this is happens about half the time. I've noticed even when I play Hoyle card games it sometimes is jerkly. I am mostly looking around Ebay so I don't know if that has anything to do with it. I absolutely never open emails with attachments or click on anything in an email. I use Norton Systemworks, Norton Firewall and I've recently used AdAware and CWShredder. I had a tech person "tune up" my computer, rid of temp. files, defragged, antivirus, etc. My computer is only 1 1/2 yrs. old. Please help me and keep in mind I know more about the Internet than I do the computer itself. This has taken all the joy out of being on line.