Specify which PB G4 1.67? The first 1.67 (DDR-333 SODIMMs), or the last one with the DL Superdrive and the HD Screen (DDR2-533 SODIMMs)?
If you are in the USA, the most often recommended vendors on MR are Crucial (see link above), OWC (MacSales) and Data Memory Systems Seaching is good, we have covered the question before . There is also a Guide about memory.