i just recently install 2 x 1 gb corsair 1066 sticks...so now i have 4 x 1gb running at 1066...its running stable at 5-5-5-15 timings

make sure u set dram voltage at 2.1V or 2.2V and gotta up the NB volts to 1.35+ for stablility....my cpu is at 3.1