Lag due to CPU UsageFollow

I noticed this first in EQ however it also happens in other non-online games. It started yesterday when every few seconds in eq I was lagging but only for a second and in non-crowded zones where I don't usually get lag. I check the cpu usage in the task manager and the usage is going from nothing to 18% and back down to 0 continually (with the same frequency as the lag). I have tried closing everything it will let me in the task manager and nothing I close makes it stop. Also the computer no longer will shut down (it says logging off and then stays there and I have to shut down with the power button on the computer). It started while I was logged onto eq however it is not exclusively eq related. I have updated the video drivers, defragmented the hard drive and tried disconnecting the cable internet connection. Thanks in advance for any help.

Oh I have a pentium 2.67 ghz, gforce2 video card.

Although I wish it was the graphics card (an excuse to get a new one) I am trying to put it off until eq2 (trying to upgrade my sons computer first with memory and stuff) I finally got the cyclical activity to stop. After running a spyware sweep program and having trouble with Norton after running the live update (I think it might have been messing with the download). I disabled everything on that automatically starts up when the computer is turned on (through msconfig). When this was done there is no more cyclical cpu usage and the lag is gone in eq except of course in POK by the bank and the Bazaar. And after getting rid of it the Norton live update no longer results in errors in the program. Not sure exactly what was happening but something was running in the background that wasnt showing up on the task manager. Although perhaps it is time for a new video card. Thanks..