Socket423 is the original Pentium 4 socket; Intel doesn't encourage use of that socket format anymore. Socket478 is the new P4 socket that Intel plans to continue supporting. When Intel releases the Northwood, it will (probably) only be available for Socket 478.
If you want a P4 system with top performance and maximum upgradeability, use a Socket478 i850-based motherboard. Asus and Abit both make such motherboards.
Kelledin
"/join #hackerz. See the Web. DoS interesting people."