i have a M2N-E motherboard from ASUS, can I install ram that run at different clock speeds?
When different speed RAM modules are used, all of the RAM should clock to the speed of the slowest module. Many times, I've found that mixing RAM speeds sometimes causes system instability. I've had plenty of cases where RAM sticks that tested just fine alone wouldn't play well together. So I strongly recommend that all of the RAM installed in your computer be of the same speed.
It depends on a lot of differents aspect, but as long your Asus motherboard supports DR2-533 / DDR2-667 / DDR2-800, I think you can try without causing troubles to your mobo.
i suppose you're referring to you other question.
you currently have 2x 512 MB 533 MHz. you can install another 2x 2 GB 800 Mhz alright and get a total of 5 GB. However, the memory will only operate at 533 MHz and you'll be far better off, performance-wise, to ditch the 2x 512 MB RAM and go with 4 GB @ 800 MHz instead.