Well the Athlon XP 2400+ is a good CPU but it´s certainly an "Thoroughbred" that is an old version from Athlon XP with an cache of L2 of just 256. After this model AMD introduced the Barton, an more strong CPU, available from AMD Athlon XP 2500+ to 3000+ with L2 Cache of 512!
The difference of price is not really big, so if you can afford it, would be a better choice to buy an AMD Athlon XP 2600+ Barton.
Abot the graphic card, Asus Geforce FX5600 has on general better performances...
If you use Hi-Speed Internet and make downloads, 40 GB of disk in nowdays very few.. try at leat one of 80GB!!
Hope i gave some help!
Safe landings,
Simão Oliveira
EHO Manager