Seems like an ok build to me actually. I was going to suggest a TX750W Corsair but in that case I'm not so sure. The 520W should be fine for the build and I'll take Corsair over any OCZ PSU any day unless it's the super high end stuff. Have you also considered a better heatsink such as the
Scythe Shuriken since in that cramped case, having a better cooler not only lowers temps but would also make for a quieter and longer lasting computer. Think you also need to factor in the cost of a keyboard too and monitor if your not reusing anything. If your budget still permits, you might as well go for the 275 but since I'm assuming your parents don't game, it might not be worth it The $200 275 at ncix is a good deal but you can always price match for
$220. Also, with 8 years of computing, and depending on their computer uses, you might have to get more than 640gb of storage. You also mention RAID hard drives but I'm not sure where your going with that either since you only have one hard drive listed. Toss in a fan or two while your at it too. I'd say a Noctua since their quiet but it's up to you whether you want silence or cooling power, the
AC PWM might not be a bad choice either