When installed together the PC3200 will downclock to the slower of the two Dimms PC2700 speed or 333Mhz. As you mentioned, there is no guarantee two mismatched DIMMs will behave together. As far as BIOS adjustments to be made, not all BIOS are the same. Basic BIOS adjustments for RAM are speed, timing and voltage, but your BIOS may not have ANY RAM adjustments available. Go in BIOS and see what's available. A bump up in RAM voltage if available may help with RAM stability.