...I guess what it comes down to, is I would need a new motherboard and power supply...
Add a video card if you still want to play modern games at a decent resolution and FPS rate. So if your current rig does not fulfill your needs, I believe you will require a new build. From a quick google of your PC, you could recyle into a new build the following:
- hard drive
- DVD drive
- and if you had to, you could probably keep the 2 GB x 2 RAM modules and motherboard
Imho, you might be better off selling your rig completely as-is (to get some $ out of it) and building a new one. A budget gaming build/everyday PC would start around $500, but can easily close on $800, depending on what you want it to do.
Or keep it and just read books! I don't know anything about "The War Z" game, but I have "World War Z", the book, in my queue