Comuter Build Help

I'm looking to upgrade my desktop from 2006 for some low to mid performance gaming (RuneScape, Minecraft, TOR, LOTRO) and have $250 to spend including shipping. I have all peripherals and a hard drive that I hope to transfer from the current system to the next as well as a CD drive.

Processor
Name-AMD Athlon 64 3500+
CodeName- ClawHammer
Package-Socket 939
Core Speed - 2210.1 MHz
Bus Speed - 200.9 MHz

Mainboard
Manufacturer - ASUSTeK Computer INC.
Model- A8N-VM-CSM Rev1.xx
NViDIA GeForce 6150 Chipset
NVIDIA nForce 410/430 MCP Southbridge
Graphic Interface Version- PCI-Express
Link Width: x16
Max. Supported x16

Memory
Type - DDR
Size- 1024 MBytes
DRAM Frequency- 200.9 MHz

DirectX Version- DirectX 9.0c
Device Name- NVIDIA GeForce 8400 GS
Approx Memory - 512.0 MB
Main Driver - nv4_disp.dll
Version - 6.14.0011.7516

The chassis is an Antec Atlas 550 and the PSU is an Antec SmartPower 2.0 SP-350 350W ATX12V.

I am willing to send pictures of the computer via cell phone to someone (hopefully you are in the US) so you can tell if the chassis is big enough to support and whether my HDD is compatible.

So, if you can find me possible ways to upgrade this desktop (CPU,GPU, RAM, Mobo) I would really appreciate it. I've checked NewEgg, but so far Ebay seems to be the best for RAM/CPU/Mobo bundles.