Dan, I'm with Piz. Drop the Norton and check with your ISP and see if they carry a free Anti-virus program which usually comes with three license keys.
Like the other fellas said, there's not much you can do to upgrade the power of your machine. You can try Game booster, Firefox, and optimizing your PC with a Googled program, and/or:
You can upgrade your RAM to 2GB
Your XP pro is OK
Look into upgrading your GPU (video card)
You need to upgrade your CPU to a 2.4 GHz at minimum
Your best bet Dan is to invest in a new PC if the time is right.
Happy new year!