Do you only need the CPU/Mobo/RAM/GPU that you listed above or do you need everything?
Assuming you need everything:
CPU/Mobo:
X3 425 and ASUS M4A77TD Combo for $124 after rebate after rebate
RAM:
Kingston ValueRAM 2 x 1GB DDR3 1066 $58
HDD:
Seagate 7200.12 500 GB $55
PSU/Optical:
Corsair 400W and cheap SATA DVD burner $60 after rebate
Case:
GIGABYTE gz-ph1a3 $20
GPU:
HD 4650 $30 after rebate
Total: $347 after rebates. This will be a lot more future proof than those configurations, and will good for gaming at your low resolution. Once you get above the 1280x1024, I make no garauntees. Due to the very low resolution, I sacrificed a little GPU power for a better CPU. When you upgrade, you will only need to upgrade the GPU and possibly the PSU (depending on the card). If you've got another $40, stick the
HD 4670 in the build for improved performance.
I highly recommend saving up a little more ($485 total) and getting this
550W PSU and HD 5770 if you have plans of upgrading the monitor to a 1900x soon.
Assuming you only need what's listed in the original post:
CPU/Mobo:
X3 425 and ASUS M4A77TD Combo for $124 after rebate after rebate
RAM:
Kingston ValueRAM 2 x 1GB DDR3 1066 $58
GPU: HD 5770 $153 after rebate
Total: $335. This will be able to game up to 1600x resolutions without a problem, and at 1920x1080 with some lowered detail, if you eventually upgrade your monitor