I do have comments about the software you're running.
Norton, (which product?), disabled. Disabling Norton doesn't stop any background processes working. If both Norton and ZA have the firewall, anti-virus, and anti-virus options and any of the Norton's options are still running in the background, you are going to see conflicts. I would completely uninstall Norton, and just keep the installer and licensing details to one side, in case ZA fails. I doubt ZA is going to 'fail' is such a catastrophic way.
Spybot S&D. Sadly, this is not the utility it once was, and the TeaTimer option is known to cause problems on today's machines and software.
Similarly with Lavasoft's AdAware.
Sort those out, and if there are still performance issues come back so others can help with suggestions or comments about the self-build or other issues.
I purchased a Intel DQ963FX motherboard and mated it with a Intel E2200 Dual core processor. I have 3 gig memory and a NVidia 9400 GT graphics card w/1 gig memory. The machine is not used for gaming but for everyday on line tasks. The on board graphics are disabled. I updated the Bios to the latest version and am running XP Pro SP3. I have the usual antivirus protection enabled, Purchased Zone internet suite, Nortons (kept disabled in case zone craps out)and malware bytes, Super anti malware, Spybot S&D and ad aware.
Sometimes when I start this machine and go to Firefox,(or IE for that matter) the system will slow to the point that even audio is stunted. I have the latest java enabled so I don't think that is the problem. This motherboard has very little in the bios to tweak so that hasn't been tampered with too much (latest bios update was installed after the slow started). Whenever the slow down occurs if I restart the machine it will run up to speed for awhile then eventually slow down again. My old P-4 3.02 was sooo much faster that I regret ever having built this new clunker. I unfortunately gave the old machine to my grand daughter. Is there a known problem with this mb or proc that I haven't found yet? Or, Is this the best I can expect from Intel? I'm considering junking this setup and starting over but with maybe a quad next time. Any help/suggestions would be greatly appreciated.