I went to a shop and saw DDR II 800 and DDR II 800 Express. I was told that the Express is better because it can run DDR 533, 667 and 800 whereas DDRII 800 can only run at 800.
I didn't get it. But then I have not used DDR II before so may be there is something new about this.
umm, you can always underclock ram from it's rated stock. never listen to the idiots who work in retail stores (though a few guys are excluded from that generalization )