If cpuz lists your ram speed over 400, then you're already running it at the max. When you overclock the cpu, the ram normally overclocks with it when the speed is set in manual mode. Cpuz lists the ram speed as half the actual speed. (533=1066). If your ram is less, try changing the memory setting from "auto" to "manual" and see if 533 is listed. But if you try overclocking the cpu with the ram speed set to 533 in manual mode, then the system may not post, then you have to reset the bios using the cmos jumper or remove the battery and start over.
Many boards won't run the ram at 1066. You may leave it at 800; the performance difference is small. Overclocking the cpu modestly without a voltage increase won't cause your system to die; it may simply freeze up or reboot on it's own. It's up to you.