If she is going to pay $500 for just RAM MB & CPU she would be better served by an modern INTEL system (cost/power/speed/efficiency) ratio.
The AMD cpu's are good, but only for budget systems (about $100 and below/CPU).
Here is my suggestion. Now with out knowing the hard drive, the Graphics Card, it is kind of hard to make a accurate recommendation, but here we go.
(Assuming she will use Windows 7 64bit. If she is using WinXP all this is over-kill.)
CPU:
http://www.newegg.com/Product/Product.a ... 6819115215 (AMD has NOTHING on this CPU) $194.99
Mother Board:
http://www.newegg.com/Product/Product.a ... 6813131604 $114.99
RAM:
http://www.newegg.com/Product/Product.a ... 6820227503 $99.99 (I doubt that she will need more than 4GB of RAM. I have 6 GB, and I hardly ever surpass 50%.)
Total of $409.97
With what is left over she could get a new Graphics card, or I would recommend this:
http://www.newegg.com/Product/Product.a ... 6822136320The harddrive's speed should not be neglected. It will be the weakest link, and will effect performance. Using an old harddrive may negate the speed of the invested system.
The system I describe has more 'speed' and efficiency per clock-rate.
This is my recommendation.
If there are any doubts, I reference this:
http://www.tomshardware.com/reviews/bes ... 675-7.htmledit: I hope that the PSU has the more modern standards to support this or other state of the art systems. You should make sure.
And the products he listed is top of the line for that budget, If she can come up with about 100 bucks more...look at these:
