I prefer to buy a computer from a store that I know even if it's a bit more expensive.
Besides, there are stores that have lower prices for parts, but charge about 40$ for building the PC.
I thought I found another possible board - Asus p4vp-mx or Asus p4ge-mx, but they don't support DDR 400, so it would be a waste.
There's also Asus p4s800-mx, but I'm not sure its sound chipset AD1888 is supported.