Probably. Older motherboards may have trouble with newer high-density RAM chips (in which case a BIOS update may help). Mixing different-speed RAMs in the same motherboard may also cause problems. You may need to clear CMOS to get the motherboard to rescan the memory (so make note of your settings before trying the new RAM).
That said, if you've got them already, try them and see. In the worst case you'll have to take them back out and clear CMOS again.