Wow, that's news to me. Didn't know that. There aren't a whole lot of Socket 478 motherboards around. I think they're fading away like dinosaurs. I can only suggest now to upgrade the motherboard entirely and the CPU to 775. Maybe get a nice Core 2 Duo CPU, PCI-express, DDR2 RAM, SATA HD, and the rest of the good stuff. That will cost much more though, but wow the PC will be much faster.
Or if he's still using DDR SDRAM, a nice motherboard and CPU upgrade are probably all he needs as you have mentioned earlier.