I have an asrock 4coredual-vsta with 2x512mb ddr400 and 7600gt agp.
Is the memory frecuency correct?I can't make it to run at 200Mhz.
This is what I get in cpu-z:

Most BIOSes have an option to set the ratio of FSB to RAM speed - you could have a look and see if you can manually set that.

Although I set it in the bios(ddr400-200mhz) I can't get (in cpu-z) the right frequency

Not sure then.

Try on the boards here: http://forums.overclockers.co.uk/

Its where I go for all my technical help.

go into the bios and set the memory divider to 1:1 meaning you should set it at 200 memory strap. therefore it will run the memory at 200mhz witch is what ddr400 is made to be run at. you will see a little difference in performance but no HUGE gain. maybe a few more fps or so.

edit: try a higher memory strap if you can i just re read one of your post and seen you've tried to run it at ddr400(200mhz) from bios. that board has overclocking options so i know it has the right option for your memory just have to play around a bit but it should be at 200mhz if you set it at 200 memory strap in bios and make sure you press F10 and then hit enter or Y to save your settings then you should be ok.