MSI's memory dividers are stated in terms of speeds. In my BIOS, at least, you select the divider by selecting a RAM speed. In my case, it's either DDR2-400, 533, 667, or 800. Each of these speeds corresponds to a different divider. For example, selecting the 800 MHz divider with a 1.9 GHz CPU will result in a /5 divider, since 1900 MHz/5=380 MHz, and 380MHz *2 is the fastest usable speed under 800 MHz. Selecting the 667 divider with the same CPU would result in the /6 divider, since (1900/6)*2 is the largest value that does not exceed 667 MHz. However, selecting the 533 divider with a 1.9 GHz CPU would result in a /8 divider since the /7 divider would produce a RAM speed of 552 MHz with a 1.9 GHz CPU...over the rated speed of 533 MHz.
That's how it is on my Socket AM2 K9N Platinum, anyway...it could be slightly different on your K8N Neo.
Also, if you took some pictures of your Cell menu, that would help since we could actually see the options present.