No in regards to the CPU (processor) I was referring to it not being worth getting anything more than a Radeon X1950 PRO, because your CPU will hold the GPU (graphics card) back.
KaleunBier I would recommend you buy everything second hand, if you have to. Have you seen the prices of AGP graphics cards?
At the end of the day, remember that you're throwing money at obselete technology and it's like throwing money down the drain in my eyes because new AGP cards are not being made and old ones are more than likely not supported for new games. Plus new games now require pixelshader 3.0 which AGP cards dont have. How long until DX 10 takes over form DX9? I read Service Pack 3 for XP is the last Pack Windows will do. People forget computers don't get old, they get obselete. Try using a Windows 98 machine with a 1.8mhz Pentium 2 with a Nvidia FX5500, today. It will hardly run the Firefox browser. Well the PC you described isn't far off that...I give it another couple of years, max.
I would just save the money you will spend on "upgrading" for a new machine..as I said, new GPU and memory will come to a third of a brand new FAST PC which you can play GWX in max settings and play SH4 if you wanted.
I saved for 3 years and now I'm luvin' it...
But if you do go ahead with it, don't expect GWX to blow you away...it will be very frustrating and you will have to play without the 16km and use the "empty harbour" mod...and it will still slow down to a crawl when you're near the harbour.