PC hardware, MY FAVORITE!!!
I can assist you, but first I need to have more info.
1. What is your budget?
2. What do you intend to do with the PC? Games, Video editing/encoding, Graphic design etc...
I have bad news for you...Chances are, unless you planning on only doing non graphic intensive applications (internet, MS Word, etc...), MS VISTA won't work neither. I'm going to recommend that you buy a new computer rather than upgrade here's why...
1. Heavy graphic applications (especially 3D, like games) run hand in hand with the CPU. If your CPU is too slow it will great a severe bottleneck on the new Graphics card in running your apps. Think of it as buying a Porsche 911 Turbo and then having drive it 30 mph. You are simply not using all the power available. For anything graphic intensive, you need a good (or at least decent) CPU. So a CPU investment is strongly recommended, which brings us to problem #2...
2. You have a major compatibility problem, both with the CPU and graphics card. Your current motherboard uses CPU Socket A, and a AGP slot. Neither are compatible with the newest hardware out there which is now AM2/Socket 775 and PCIe.
Upgrading the CPU alone means replacing the CPU, motherboard, RAM, video card (might as well kill 2 birds with 1 stone) and the PSU. Thats almost a new computer right there...
Upgrading the CPU alone means you will have to get a new video card that uses AGP (and not PCIe). Today, there are almost no new cards that use AGP and the ones out there are VERY EXPENSIVE and MUCH SLOWER than the PCIe ones. To get a modest speed increase, you'll have to spend $300-$400 on a tech thats already dead and buried.
That is not a wise investment, I strongly discourage you from this.
You could get a complete Dell system starting at $350 without tax which will be slow be todays standards but will still run rings around your current rig and whatever AGP card you buy for your old system.
Talk to me before you buy anything...
business for sale by ownerr4i