Building a Machine for Contractor

Hi folks, I'm looking at building a machine for a building contractor.
I'm thinking Phenom II X4 with at least 4GB of RAM. I'd like to avoid
built in video if that's possible. Also, I'm thinking a mirrored RAID 1
volume.
Let's shoot for $300(US) without the monitor for starters.
Once I get some specs from the internets I'll tweak it. The case can be
somewhat plain as this is going to be a business machine.
I'm a bit behind on the latest hardware so bear with me!

Justin