Based on what I (can't) find for your motherboard, it's probably best to just toss the motherboard, CPU and RAM and buy those from scratch. You can do a fairly decent mATX AMD board and a dual or quad core AMD + 4GB of RAM for about the price you're stating. Sadly, the video card can't be reused, but even some of today's onboard chips are better than that FX5200 you have.
What is your upper limit as far as funds go?
Here's what I could do: (Prices are US $)
Motherboard: Newegg.com - MSI 760GM-E51 AM3 AMD 760G HDMI Micro ATX AMD Motherboard
RAM: Newegg.com - Patriot 4GB (2 x 2GB) 240-Pin DDR3 SDRAM DDR3 1333 (PC3 10600) Desktop Memory Model PSD34G1333K
CPU: Newegg.com - AMD Phenom II X4 945 Deneb 3.0GHz 4 x 512KB L2 Cache 6MB L3 Cache Socket AM3 95W Quad-Core Desktop Processor HDX945WFGMBOX
Total in US: $244.97
The CPU has more than enough horsepower for what you'd like to do, and helps keep you as up to date as possible, the motherboard while not top of the line is basically the same integrated AMD GPU as on the newer 8x series chipsets, and the RAM should be more than enough for a while. The motherboard would support your old hard drive, but you'd have to buy a new CDROM to plug into SATA, but those are cheap enough. If you really want to add more speed to the system, getting a modern 500 GB+ hard drive for about $40 on top of this would help things out a lot (in addition to the CDROM upgrade)
So not too bad, but there's a place to start.