Joe, for what it's worth, I just built a computer for photo work. I live in Mexico so some of my options are limited. I am assume that since you are building the computer and selecting the components, you're mom is low on the geek scale and won't want to spend time on computer issues.
My computer is similar to what you built. Due to taxes here, my processor is a P6550. I got 4Gb or RAM. Two 500Gb 7200rpm hard drives. I am using an Intel motherboard, DP35DP with the same chipset as your ASUS, I think.
The differences? I don't use a RAID array. For me, backing up to DVDs is routine and it just isn't worth the hassle. If I had a RAID1, I would still back up to DVD.
I love dual monitors so I got two 22" LCD monitors. For me, it's great for editing photos--and other stuff.
The stock cooling system is working fine and I didn't need any thermal paste. I did get a "gaming" case so I have five fans but I live in the tropics, too.
I run Vista 32.