I'm not sure what 100 mc = 1 BTC/NMC means, since bitcoins are different from namecoins, and the ratio of them isn't a meaningful store of value . . .
That means that 1 BTC = mooncoins (bitcoin mooncoins) or 1 NMC = 100 mooncoins (namecoin mooncoins). They are segregated throughout the whole site and you maintain two different balances.
The idea about the * 100 is to make it easier to bet if you have smaller amounts of coins.
Two different currencies with the same name seems needlessly confusing to me. You already have an exchange on the site, so why not consolidate into one currency: make 1 mooncoin = 1 USD? Then anyone betting on your site is not ALSO betting on the value of an e-currency rising.
Best of luck to you . . .