Your memory can potentially run at the highest clock speed your motherboard supports.
If your motherboard supports 1066, then your memory on autoselect, should be running at 1066.
If your motherboard only supports 667, then your memory will be running at 667, if at all.
If your motherboard supports 1333, and your memory is 1066, then it is running at 1066.
I wouldn't really OC memory/and FSBs too much unless ya know what you're doing.
As for determining what your memory is operating at, somewhere in your BIOS it will probably indicate the speeds.