New Computer Help

I am really itching to buy a new computer, but am on a tight budget. I currently am trying to game with a used computer I bought at auction (not a bad rig, it’s 2.8 GHz, 1 GB RAM and GEForce 5500 vid card). It just isn’t cutting it, tho. I was looking at Dell and found a system with a processor option of either an Pentium? D Processor 915 or a Pentium? D Processor 820. I thought I looked everywhere to find the difference, but couldn’t. Should I spend the extra $65 for the 915? Is it worth it? I plan on getting a better graphics card and about 2GB of RAM.

Also, is gaming with Windows Media Center Edition ok? I’ve never tried it before.

Thanks