Crucial 2GB (2 x 1GB) DDR2 SDRAM DDR2 667 (PC2 5300) Dual Channel Kit CAS 3

[nicepun]

tried 3-3-3-8, 3-4-3-8, & 3-4-4-12 with voltages from 2.25-2.45, loosening subtimings didn't help either
max voltage on the P5B is 2.45V

Have you tried DDR2-1000 @ CAS 4?