DDR Memory Question

currently I have two 128 mb sticks of DDR1600 in my computer.

I wanna go to 512. Right now a 256 MB DDR2100 chip is cheaper than DDR1600 but will it work? I remember with older memory it just all ran at the slowest speed chip. Does that hold true with DDR as well?

yea ddr is bkwards compatible

i have an a7n266-e and i have 256 of pc2700 and 768 of pc2100 (accidently bought the 256 of 2700 when i was first assembling computer)

works fine