Well, you currently have a S478 Willy if I am not mistaken. Your board determines how fast of a CPU you can stick in there.
If it's a 400FSB-only board, you can put up to a 2.8 Northwood A in there.
If it's a 400/533FSB board, you can put up to a 3.06 Northwood B in there.
If it's a 400/533/800FSB board, you can out up to a 3.4 Northwood C in there.