I used to say you don't need 8GB of RAM.  Now that I have been running 4 rigs with 8GB of RAM for a week, I realize why people do it.  The system just runs that much more stable.  Things don't seem as laggy when I'm remoted in from another location either.

If you can spend a little more and get a Pentium CPU, I would do that too.  I paid $40usd for my Celeron ... I think the Pentium was $52.  It's not that much more money.